hesim: Health Economic Simulation Modeling and Decision Analysis

Description

To learn more about hesim visit the website.

Author(s)

Maintainer: Devin Incerti devin.incerti@gmail.com

Authors:

• Jeroen P. Jansen

• Mark Clements

Other contributors:

• R Core Team (hesim uses some slightly modified C functions from base R) [contributor]

See Also

Useful links:

• https://hesim-dev.github.io/hesim/

• https://github.com/hesim-dev/hesim

• Report bugs at https://github.com/hesim-dev/hesim/issues

Cohort discrete time state transition model

Description

Simulate outcomes from a cohort discrete time state transition model.

Format

An R6::R6Class object.

Public fields

Methods

Public methods

• CohortDtstm$new()

• CohortDtstm$sim_stateprobs()

• CohortDtstm$sim_qalys()

• CohortDtstm$sim_costs()

• CohortDtstm$summarize()

• CohortDtstm$clone()

Method new()

Create a new CohortDtstm object.

Usage

CohortDtstm$new(trans_model = NULL, utility_model = NULL, cost_models = NULL)

Arguments

Returns

A new CohortDtstm object.

Method sim_stateprobs()

Simulate health state probabilities using CohortDtstmTrans$sim_stateprobs().

Usage

CohortDtstm$sim_stateprobs(n_cycles)

Arguments

Returns

An instance of self with simulated output of class stateprobs stored in stateprobs_.

Method sim_qalys()

Simulate quality-adjusted life-years (QALYs) as a function of stateprobs_ and utility_model. See sim_qalys() for details.

Usage

CohortDtstm$sim_qalys(
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right"),
  lys = TRUE
)

Arguments

Returns

An instance of self with simulated output of class qalys stored in qalys_.

Method sim_costs()

Simulate costs as a function of stateprobs_ and cost_models. See sim_costs() for details.

Usage

CohortDtstm$sim_costs(
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right")
)

Arguments

Returns

An instance of self with simulated output of class costs stored in costs_.

Method summarize()

Summarize costs and QALYs so that cost-effectiveness analysis can be performed. See summarize_ce().

Usage

CohortDtstm$summarize(by_grp = FALSE)

Arguments

Method clone()

The objects of this class are cloneable with this method.

Usage

CohortDtstm$clone(deep = FALSE)

Arguments

References

Incerti and Jansen (2021). See Section 2.1 for a description of a cohort DTSTM and details on simulating costs and QALYs from state probabilities. An example in oncology is provided in Section 4.3.

See Also

CohortDtstm objects can be created from model objects as documented in create_CohortDtstm(). The CohortDtstmTrans documentation describes the class for the transition model and the StateVals documentation describes the class for the cost and utility models. A CohortDtstmTrans object is typically created using create_CohortDtstmTrans().

There are currently three relevant vignettes. vignette("markov-cohort") details a relatively simple Markov model and vignette("markov-inhomogeneous-cohort") describes a more complex time inhomogeneous model in which transition probabilities vary in every model cycle. The vignette("mlogit") shows how a transition model can be parameterized using a multinomial logistic regression model when transition data is collected at evenly spaced intervals.

Examples

library("data.table")
library("ggplot2")
theme_set(theme_bw())
set.seed(102)

# NOTE: This example replicates the "Simple Markov cohort model" 
# vignette using a different approach. Here, we explicitly construct
# the transition probabilities "by hand". In the vignette, the transition 
# probabilities are defined using expressions (i.e., by using 
# `define_model()`). The `define_model()` approach does (more or less) what 
# is done here under the hood.

# (0) Model setup
hesim_dat <- hesim_data(
  strategies = data.table(
    strategy_id = 1:2,
    strategy_name = c("Monotherapy", "Combination therapy")
  ),
  patients <- data.table(patient_id = 1),
  states = data.table(
    state_id = 1:3,
    state_name = c("State A", "State B", "State C")
  )
)
n_states <- nrow(hesim_dat$states) + 1
labs <- get_labels(hesim_dat)

# (1) Parameters
n_samples <- 10 # Number of samples for PSA

## Transition matrix
### Input data (one transition matrix for each parameter sample,
###             treatment strategy, patient, and time interval)
p_id <- tpmatrix_id(expand(hesim_dat, times = c(0, 2)), n_samples)
N <- nrow(p_id)

### Transition matrices (one for each row in p_id)
p <- array(NA, dim = c(n_states, n_states, nrow(p_id)))

#### Baseline risk
trans_mono <- rbind(
  c(1251, 350, 116, 17),
  c(0, 731, 512, 15),
  c(0, 0, 1312, 437),
  c(0, 0, 0, 469)
)
mono_ind <- which(p_id$strategy_id == 1 | p_id$time_id == 2)
p[,, mono_ind] <- rdirichlet_mat(n = 2, trans_mono)

#### Apply relative risks
combo_ind <- setdiff(1:nrow(p_id), mono_ind)
lrr_se <- (log(.710) - log(.365))/(2 * qnorm(.975))
rr <- rlnorm(n_samples, meanlog = log(.509), sdlog = lrr_se)
rr_indices <- list( # Indices of transition matrix to apply RR to
  c(1, 2), c(1, 3), c(1, 4),
  c(2, 3), c(2, 4),
  c(3, 4)
)
rr_mat <- matrix(rr, nrow = n_samples, ncol = length(rr_indices))
p[,, combo_ind] <- apply_rr(p[, , mono_ind],
                            rr = rr_mat,
                            index = rr_indices)
tp <- tparams_transprobs(p, p_id)

## Utility
utility_tbl <- stateval_tbl(
  data.table(
    state_id = 1:3,
    est = c(1, 1, 1)
  ),
  dist = "fixed"
)

## Costs
drugcost_tbl <- stateval_tbl(
  data.table(
    strategy_id = c(1, 1, 2, 2),
    time_start = c(0, 2, 0, 2),
    est = c(2278, 2278, 2278 + 2086.50, 2278)
  ),
  dist = "fixed"
)

dmedcost_tbl <- stateval_tbl(
  data.table(
    state_id = 1:3,
    mean = c(A = 1701, B = 1774, C = 6948),
    se = c(A = 1701, B = 1774, C = 6948)
  ),
  dist = "gamma"
)

cmedcost_tbl <- stateval_tbl(
  data.table(
    state_id = 1:3,
    mean = c(A = 1055, B = 1278, C = 2059),
    se = c(A = 1055, B = 1278, C = 2059)
  ),
  dist = "gamma"
)

# (2) Simulation
## Constructing the economic model
### Transition probabilities
transmod <- CohortDtstmTrans$new(params = tp)

### Utility
utilitymod <- create_StateVals(utility_tbl,
                               hesim_data = hesim_dat,
                               n = n_samples)

### Costs
drugcostmod <- create_StateVals(drugcost_tbl,
                                hesim_data = hesim_dat,
                                n = n_samples)
dmedcostmod <- create_StateVals(dmedcost_tbl,
                                hesim_data = hesim_dat,
                                n = n_samples)
cmedcostmod <- create_StateVals(cmedcost_tbl,
                                hesim_data = hesim_dat,
                                n = n_samples)
costmods <- list(drug = drugcostmod,
                 direct_medical = dmedcostmod,
                 community_medical = cmedcostmod)

### Economic model
econmod <- CohortDtstm$new(trans_model = transmod,
                           utility_model = utilitymod,
                           cost_models = costmods)

## Simulating outcomes
econmod$sim_stateprobs(n_cycles = 20)
autoplot(econmod$stateprobs_, ci = TRUE, ci_style = "ribbon",
         labels = labs)
econmod$sim_qalys(dr = 0, integrate_method = "riemann_right")
econmod$sim_costs(dr = 0.06, integrate_method = "riemann_right")

# (3) Decision analysis
ce_sim <- econmod$summarize()
wtp <- seq(0, 25000, 500)
cea_pw_out <- cea_pw(ce_sim, comparator = 1, dr_qalys = 0, dr_costs = .06,
                     k = wtp)
format(icer(cea_pw_out))

Transitions for a cohort discrete time state transition model

Description

Simulate health state transitions in a cohort discrete time state transition model.

Format

An R6::R6Class object.

Public fields

Active bindings

Methods

Public methods

• CohortDtstmTrans$new()

• CohortDtstmTrans$sim_stateprobs()

• CohortDtstmTrans$clone()

Method new()

Create a new CohortDtstmTrans object.

Usage

CohortDtstmTrans$new(
  params,
  input_data = NULL,
  trans_mat = NULL,
  start_stateprobs = NULL,
  cycle_length = 1,
  absorbing = NULL
)

Arguments

Returns

A new CohortDtstmTrans object.

Method sim_stateprobs()

Simulate probability of being in each health state during each model cycle.

Usage

CohortDtstmTrans$sim_stateprobs(n_cycles)

Arguments

Returns

An object of class stateprobs.

Method clone()

The objects of this class are cloneable with this method.

Usage

CohortDtstmTrans$clone(deep = FALSE)

Arguments

See Also

create_CohortDtstmTrans() creates a CohortDtstmTrans object from either a fitted statistical model or a parameter object. A complete economic model can be implemented with the CohortDtstm class.

Examples

library("msm")
library("data.table")
set.seed(101)

# We consider two examples that have the same treatment strategies and patients.
# One model is parameterized by fitting a multi-state model with the "msm"
# package; in the second model, the parameters are entered "manually" with
# a "params_mlogit_list" object.

# MODEL SETUP
strategies <- data.table(
  strategy_id = c(1, 2, 3),
  strategy_name = c("SOC", "New 1", "New 2")
)
patients <- data.table(patient_id = 1:2)
hesim_dat <- hesim_data(
  strategies = strategies,
  patients = patients
)

# EXAMPLE #1: msm
## Fit multi-state model with panel data via msm
qinit <- rbind(
  c(0, 0.28163, 0.01239),
  c(0, 0, 0.10204),
  c(0, 0, 0)
)
fit <- msm(state_id ~ time, subject = patient_id,
           data = onc3p[patient_id %in% sample(patient_id, 100)],
           covariates = list("1-2" =~ strategy_name),
           qmatrix = qinit)

## Simulation model
transmod_data <- expand(hesim_dat)
transmod <- create_CohortDtstmTrans(fit,
                                    input_data = transmod_data,
                                    cycle_length = 1/2,
                                    fixedpars = 2,
                                    n = 2)
transmod$sim_stateprobs(n_cycles = 2)

# EXAMPLE #2: params_mlogit_list
## Input data
transmod_data[, intercept := 1]
transmod_data[, new1 := ifelse(strategy_name == "New 1", 1, 0)]
transmod_data[, new2 := ifelse(strategy_name == "New 2", 1, 0)]

## Parameters
n <- 10
transmod_params <- params_mlogit_list(
  
  ## Transitions from stable state (stable -> progression, stable -> death)
  stable = params_mlogit(
    coefs = list(
      progression = data.frame(
        intercept = rnorm(n, -0.65, .1),
        new1 = rnorm(n, log(.8), .02),
        new2 = rnorm(n, log(.7, .02))
      ),
      death = data.frame(
        intercept = rnorm(n, -3.75, .1),
        new1 = rep(0, n),
        new2 = rep(0, n)
      )
    )
  ),
  
  ## Transition from progression state (progression -> death)
  progression = params_mlogit(
    coefs = list(
      death = data.frame(
        intercept = rnorm(n, 2.45, .1),
        new1 = rep(0, n),
        new2 = rep(0, n)
      )
    )
  )
)
transmod_params

## Simulation model
tmat <- rbind(c(0, 1, 2),
              c(NA, 0, 1),
              c(NA, NA, NA))
transmod <- create_CohortDtstmTrans(transmod_params, 
                                    input_data = transmod_data,
                                    trans_mat = tmat, cycle_length = 1)
transmod$sim_stateprobs(n_cycles = 2)

An R6 base class for continuous time state transition models

Description

Contains methods that can be used to summarize both individual- and cohort-level continuous time state transition models. That is, this class is relevant for both Markov and semi-Markov multi-state models and does not depend on the methodology used for prediction of state probabilities.

Format

An R6::R6Class object.

Methods

Public methods

• CtstmTrans$hazard()

• CtstmTrans$cumhazard()

• CtstmTrans$clone()

Method hazard()

Predict the hazard functions for each health state transition.

Usage

CtstmTrans$hazard(t)

Arguments

Returns

A data.table with columns transition_id, sample, strategy_id, grp_id, t, and hazard.

Method cumhazard()

Predict the cumulative hazard functions for each health state transition.

Usage

CtstmTrans$cumhazard(t)

Arguments

Returns

A data.table with columns transition_id, sample, strategy_id, grp_id, t, and cumhazard.

Method clone()

The objects of this class are cloneable with this method.

Usage

CtstmTrans$clone(deep = FALSE)

Arguments

See Also

create_IndivCtstmTrans(), IndivCtstmTrans

Individual-level continuous time state transition model

Description

Simulate outcomes from an individual-level continuous time state transition model (CTSTM). The class supports "clock-reset" (i.e., semi-Markov), "clock-forward" (i.e., Markov), and mixtures of clock-reset and clock-forward multi-state models as described in IndivCtstmTrans.

Format

An R6::R6Class object.

Public fields

Methods

Public methods

• IndivCtstm$new()

• IndivCtstm$sim_disease()

• IndivCtstm$sim_stateprobs()

• IndivCtstm$sim_qalys()

• IndivCtstm$sim_costs()

• IndivCtstm$summarize()

• IndivCtstm$clone()

Method new()

Create a new IndivCtstm object.

Usage

IndivCtstm$new(trans_model = NULL, utility_model = NULL, cost_models = NULL)

Arguments

Returns

A new IndivCtstm object.

Method sim_disease()

Simulate disease progression (i.e., individual trajectories through a multi-state model) using IndivCtstmTrans$sim_disease().

Usage

IndivCtstm$sim_disease(max_t = 100, max_age = 100, progress = NULL)

Arguments

Returns

An instance of self with simulated output stored in disprog_.

Method sim_stateprobs()

Simulate health state probabilities as a function of time using the simulation output stored in disprog.

Usage

IndivCtstm$sim_stateprobs(t)

Arguments

Returns

An instance of self with simulated output of class stateprobs stored in stateprobs_.

Method sim_qalys()

Simulate quality-adjusted life-years (QALYs) as a function of disprog_ and utility_model.

Usage

IndivCtstm$sim_qalys(
  dr = 0.03,
  type = c("predict", "random"),
  lys = TRUE,
  by_patient = FALSE
)

Arguments

Returns

An instance of self with simulated output of class qalys stored in qalys_.

Method sim_costs()

Simulate costs as a function of disprog_ and cost_models.

Usage

IndivCtstm$sim_costs(
  dr = 0.03,
  type = c("predict", "random"),
  by_patient = FALSE,
  max_t = Inf
)

Arguments

Returns

An instance of self with simulated output of class costs stored in costs_.

Method summarize()

Summarize costs and QALYs so that cost-effectiveness analysis can be performed. See summarize_ce().

Usage

IndivCtstm$summarize(by_grp = FALSE)

Arguments

Method clone()

The objects of this class are cloneable with this method.

Usage

IndivCtstm$clone(deep = FALSE)

Arguments

References

Incerti and Jansen (2021). See Section 2.2 for a mathematical description of an individual-level CTSTM and Section 4.1 for an example in oncology.

See Also

The IndivCtstmTrans documentation describes the class for the transition model and the StateVals documentation describes the class for the cost and utility models. An IndivCtstmTrans object is typically created using create_IndivCtstmTrans().

There are currently two relevant vignettes. vignette("mstate") shows how to parameterize IndivCtstmTrans objects in cases where patient-level data is available by fitting a multi-state models. vignette("markov-inhomogeneous-indiv") shows how the time inhomogeneous Markov cohort model in vignette("markov-inhomogeneous-cohort") can be developed as an individual patient simulation; in doing so, it shows how IndivCtstm models can be used even without access to patient-level data.

Examples

library("flexsurv")

# Treatment strategies, target population, and model structure
strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3),
                       age = c(45, 50, 60),
                       female = c(0, 0, 1))
states <- data.frame(state_id = c(1, 2))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)

# Parameter estimation
## Multi-state model
tmat <- rbind(c(NA, 1, 2),
              c(3, NA, 4),
              c(NA, NA, NA))
fits <- vector(length = max(tmat, na.rm = TRUE), mode = "list")
surv_dat <- data.frame(mstate3_exdata$transitions)
for (i in 1:length(fits)){
  fits[[i]] <- flexsurvreg(Surv(years, status) ~ factor(strategy_id),
                           data = surv_dat,
                           subset = (trans == i),
                           dist = "weibull")
}
fits <- flexsurvreg_list(fits)

## Utility
utility_tbl <- stateval_tbl(data.frame(state_id = states$state_id,
                                       mean = mstate3_exdata$utility$mean,
                                       se = mstate3_exdata$utility$se),
                            dist = "beta")
## Costs
drugcost_tbl <- stateval_tbl(data.frame(strategy_id = strategies$strategy_id,
                                        est = mstate3_exdata$costs$drugs$costs),
                             dist = "fixed")
medcost_tbl <- stateval_tbl(data.frame(state_id = states$state_id,
                                       mean = mstate3_exdata$costs$medical$mean,
                                       se = mstate3_exdata$costs$medical$se),
                            dist = "gamma")

# Economic model
n_samples = 2

## Construct model
### Transitions
transmod_data <- expand(hesim_dat)
transmod <- create_IndivCtstmTrans(fits, input_data = transmod_data,
                                   trans_mat = tmat,
                                   n = n_samples)

### Utility
utilitymod <- create_StateVals(utility_tbl, n = n_samples, hesim_data = hesim_dat)

### Costs
drugcostmod <- create_StateVals(drugcost_tbl, n = n_samples, hesim_data = hesim_dat)
medcostmod <- create_StateVals(medcost_tbl, n = n_samples, hesim_data = hesim_dat)
costmods <- list(drugs = drugcostmod,
                 medical = medcostmod)

### Combine
ictstm <- IndivCtstm$new(trans_model = transmod,
                         utility_model = utilitymod,
                         cost_models = costmods)


## Simulate outcomes
head(ictstm$sim_disease()$disprog_)
head(ictstm$sim_stateprobs(t = c(0, 5, 10))$stateprobs_[t == 5])
ictstm$sim_qalys(dr = .03)
ictstm$sim_costs(dr = .03)

### Summarize cost-effectiveness
ce <- ictstm$summarize()
head(ce)
format(summary(ce), pivot_from = "strategy")

Transitions for an individual-level continuous time state transition model

Description

Simulate health state transitions in an individual-level continuous time state transition model using parameters from a multi-state model.

Format

An R6::R6Class object.

Super class

hesim::CtstmTrans -> IndivCtstmTrans

Public fields

Methods

Public methods

• IndivCtstmTrans$new()

• IndivCtstmTrans$sim_disease()

• IndivCtstmTrans$sim_stateprobs()

• IndivCtstmTrans$check()

• IndivCtstmTrans$clone()

Method new()

Create a new IndivCtstmTrans object.

Usage

IndivCtstmTrans$new(
  params,
  input_data,
  trans_mat,
  start_state = 1,
  start_age = 38,
  death_state = NULL,
  clock = c("reset", "forward", "mix", "mixt"),
  reset_states = NULL,
  transition_types = NULL
)

Arguments

Returns

A new IndivCtstmTrans object.

Method sim_disease()

Simulate disease progression (i.e., individual trajectories through a multi-state model using an individual patient simulation).

Usage

IndivCtstmTrans$sim_disease(max_t = 100, max_age = 100, progress = NULL)

Arguments

Returns

An object of class disprog.

Method sim_stateprobs()

Simulate health state probabilities from a disprog object.

Usage

IndivCtstmTrans$sim_stateprobs(t, disprog = NULL, ...)

Arguments

Returns

An object of class stateprobs.

Method check()

Input validation for class. Checks that fields are the correct type.

Usage

IndivCtstmTrans$check()

Method clone()

The objects of this class are cloneable with this method.

Usage

IndivCtstmTrans$clone(deep = FALSE)

Arguments

See Also

IndivCtstmTrans objects are conveniently created from either fitted models or parameter objects with create_IndivCtstmTrans(). A complete economic model can be implemented with the IndivCtstm class.

Examples

library("flexsurv")

# Simulation data
strategies <- data.frame(strategy_id = c(1, 2, 3))
patients <- data.frame(patient_id = seq(1, 3),
                       age = c(45, 50, 60),
                       female = c(0, 0, 1))

# Multi-state model with transition specific models
tmat <- rbind(c(NA, 1, 2),
              c(NA, NA, 3),
              c(NA, NA, NA))
fits <- vector(length = max(tmat, na.rm = TRUE), mode = "list")
for (i in 1:length(fits)){
  fits[[i]] <- flexsurvreg(Surv(years, status) ~ 1,
                           data = bosms3[bosms3$trans == i, ],
                           dist = "exp")
}
fits <- flexsurvreg_list(fits)

# Simulation model
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients)
fits_data <- expand(hesim_dat)
transmod <- create_IndivCtstmTrans(fits, input_data = fits_data,
                                   trans_mat = tmat,
                                   n = 2)
head(transmod$hazard(c(1, 2, 3)))
head(transmod$cumhazard(c(1, 2, 3)))

## Simulate disease progression and state probabilities together
transmod$sim_stateprobs(t = c(0, 5, 10))[t == 5]

## Simulate disease progression and state probabilities separately
disprog <- transmod$sim_disease(max_t = 10)
transmod$sim_stateprobs(t = c(0, 5, 10), disprog = disprog)[t == 5]

N-state partitioned survival model

Description

Simulate outcomes from an N-state partitioned survival model.

Format

An R6::R6Class object.

Public fields

Methods

Public methods

• Psm$new()

• Psm$sim_survival()

• Psm$sim_stateprobs()

• Psm$sim_qalys()

• Psm$sim_costs()

• Psm$summarize()

• Psm$clone()

Method new()

Create a new Psm object.

Usage

Psm$new(survival_models = NULL, utility_model = NULL, cost_models = NULL)

Arguments

Details

n_states is set equal to the number of survival models plus one.

Returns

A new Psm object.

Method sim_survival()

Simulate survival curves as a function of time using PsmCurves$survival().

Usage

Psm$sim_survival(t)

Arguments

Returns

An instance of self with simulated output from PsmCurves$survival() stored in survival_.

Method sim_stateprobs()

Simulate health state probabilities from survival_ using a partitioned survival analysis.

Usage

Psm$sim_stateprobs()

Returns

An instance of self with simulated output of class stateprobs stored in stateprobs_.

Method sim_qalys()

Simulate quality-adjusted life-years (QALYs) as a function of stateprobs_ and utility_model. See sim_qalys() for details.

Usage

Psm$sim_qalys(
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right"),
  lys = TRUE
)

Arguments

Returns

An instance of self with simulated output of class qalys stored in qalys_.

Method sim_costs()

Simulate costs as a function of stateprobs_ and cost_models. See sim_costs() for details.

Usage

Psm$sim_costs(
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right")
)

Arguments

Returns

An instance of self with simulated output of class costs stored in costs_.

Method summarize()

Summarize costs and QALYs so that cost-effectiveness analysis can be performed. See summarize_ce().

Usage

Psm$summarize(by_grp = FALSE)

Arguments

Method clone()

The objects of this class are cloneable with this method.

Usage

Psm$clone(deep = FALSE)

Arguments

References

Incerti and Jansen (2021). See Section 2.3 for a mathematical description of a PSM and Section 4.2 for an example in oncology. The mathematical approach used to simulate costs and QALYs from state probabilities is described in Section 2.1.

See Also

The PsmCurves documentation describes the class for the survival models and the StateVals documentation describes the class for the cost and utility models. A PsmCurves object is typically created using create_PsmCurves(). The PsmCurves documentation provides an example in which the model is parameterized from parameter objects (i.e., without having the patient-level data required to fit a model with R). A longer example is provided in vignette("psm").

Examples

library("flexsurv")
library("ggplot2")
theme_set(theme_bw())

# Model setup
strategies <- data.frame(strategy_id = c(1, 2, 3),
                         strategy_name = paste0("Strategy ", 1:3))
patients <- data.frame(patient_id = seq(1, 3),
                       age = c(45, 50, 60),
                       female = c(0, 0, 1))
states <- data.frame(state_id =  seq(1, 3),
                     state_name = paste0("State ", seq(1, 3)))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)
labs <- c(
  get_labels(hesim_dat),
  list(curve = c("Endpoint 1" = 1,
                 "Endpoint 2" = 2,
                 "Endpoint 3" = 3))
)
n_samples <- 2

# Survival models
surv_est_data <- psm4_exdata$survival
fit1 <- flexsurvreg(Surv(endpoint1_time, endpoint1_status) ~ factor(strategy_id),
                    data = surv_est_data, dist = "exp")
fit2 <- flexsurvreg(Surv(endpoint2_time, endpoint2_status) ~ factor(strategy_id),
                    data = surv_est_data, dist = "exp")
fit3 <- flexsurvreg(Surv(endpoint3_time, endpoint3_status) ~ factor(strategy_id),
                    data = surv_est_data, dist = "exp")
fits <- flexsurvreg_list(fit1, fit2, fit3)

surv_input_data <- expand(hesim_dat, by = c("strategies", "patients"))
psm_curves <- create_PsmCurves(fits, input_data = surv_input_data,
                               uncertainty = "bootstrap", est_data = surv_est_data,
                               n = n_samples)

# Cost model(s)
cost_input_data <- expand(hesim_dat, by = c("strategies", "patients", "states"))
fit_costs_medical <- lm(costs ~ female + state_name,
                        data = psm4_exdata$costs$medical)
psm_costs_medical <- create_StateVals(fit_costs_medical,
                                      input_data = cost_input_data,
                                      n = n_samples)

# Utility model
utility_tbl <- stateval_tbl(tbl = data.frame(state_id = states$state_id,
                                             min = psm4_exdata$utility$lower,
                                             max = psm4_exdata$utility$upper),
                            dist = "unif")
psm_utility <- create_StateVals(utility_tbl, n = n_samples,
                                hesim_data = hesim_dat)

# Partitioned survival decision model
psm <- Psm$new(survival_models = psm_curves,
               utility_model = psm_utility,
               cost_models = list(medical = psm_costs_medical))
psm$sim_survival(t = seq(0, 5, 1/12))
autoplot(psm$survival_, labels = labs, ci = FALSE, ci_style = "ribbon")
psm$sim_stateprobs()
autoplot(psm$stateprobs_, labels = labs)
psm$sim_costs(dr = .03)
head(psm$costs_)
head(psm$sim_qalys(dr = .03)$qalys_)

Partitioned survival curves

Description

Summarize N-1 survival curves for an N-state partitioned survival model.

Format

An R6::R6Class object.

Public fields

Methods

Public methods

• PsmCurves$new()

• PsmCurves$hazard()

• PsmCurves$cumhazard()

• PsmCurves$survival()

• PsmCurves$rmst()

• PsmCurves$quantile()

• PsmCurves$check()

• PsmCurves$clone()

Method new()

Create a new PsmCurves object.

Usage

PsmCurves$new(params, input_data)

Arguments

Returns

A new PsmCurves object.

Method hazard()

Predict the hazard function for each survival curve as a function of time.

Usage

PsmCurves$hazard(t)

Arguments

Returns

A data.table with columns sample, strategy_id, patient_id, grp_id, curve (the curve number), t, and hazard.

Method cumhazard()

Predict the cumulative hazard function for each survival curve as a function of time.

Usage

PsmCurves$cumhazard(t)

Arguments

Returns

A data.table with columns sample, strategy_id, patient_id, grp_id, curve, t, and cumhazard.

Method survival()

Predict survival probabilities for each survival curve as a function of time.

Usage

PsmCurves$survival(t)

Arguments

Returns

An object of class survival.

Method rmst()

Predict the restricted mean survival time up until time points t for each survival curve.

Usage

PsmCurves$rmst(t, dr = 0)

Arguments

Returns

A data.table with columns sample, strategy_id, patient_id, grp_id, curve, t, and rmst.

Method quantile()

Predict quantiles of the survival distribution for each survival curve.

Usage

PsmCurves$quantile(p)

Arguments

Returns

A data.table with columns sample, strategy_id, patient_id, grp_id, curve, p and quantile.

Method check()

Input validation for class. Checks that fields are the correct type.

Usage

PsmCurves$check()

Method clone()

The objects of this class are cloneable with this method.

Usage

PsmCurves$clone(deep = FALSE)

Arguments

See Also

PsmCurves are conveniently created from either fitted models or parameter objects with create_PsmCurves(). A complete economic model can be implemented with the Psm class. A longer example is provided in vignette("psm").

Examples

library("flexsurv")
N_SAMPLES <- 5 # Number of parameter samples for PSA

# Consider a 3-state model where there is a 
# progression-free survival (PFS) and an
# overall survival (OS) endpoint

# (0) Model setup
hesim_dat <- hesim_data(
  strategies = data.frame(
    strategy_id = c(1, 2),
    strategy_name = c("SOC", "New 1")
  ),
  patients = data.frame(
    patient_id = 1
  )
)

# (1) Parameterize survival models
## (1.1) If patient-level data is available, 
## we can fit survival models

### (1.1.1) Data for estimation (for simplicity, only use 2 strategies)
surv_est_data <- as_pfs_os(
  onc3[strategy_name != "New 2"], 
  patient_vars = c("patient_id", "strategy_name")
)
surv_est_data$strategy_name <- droplevels(surv_est_data$strategy_name)

### (1.1.2) Fit models
fit_pfs <- flexsurvreg(Surv(pfs_time, pfs_status) ~ strategy_name,
                       data = surv_est_data, dist = "exp")
fit_os <- flexsurvreg(Surv(os_time, os_status) ~ strategy_name,
                      data = surv_est_data, dist = "exp")
fits <- flexsurvreg_list(pfs = fit_pfs, os = fit_os)

## (1.2) If patient-level data is NOT available, 
## we can construct the parameter objects "manually"

### (1.2.1) Baseline hazard:
### Assume that we know the (log) rate parameters for both PFS and OS 
### for SOC (i.e., the intercept) and their standard error
logint_pfs_est <- -1.7470900
logint_pfs_se <-  0.03866223
logint_os_est <- -2.7487675
logint_os_se <- 0.04845015

### (1.2.2) Relative treatment effect:
### Assume we know the log hazard ratios (and their standard errors) 
### for comparing the new interventions to the SOC
loghr_pfs_est_new1 <- -0.1772028 
loghr_pfs_se_new1 <- 0.05420119
loghr_os_est_new1 <- -0.1603632
loghr_os_se_new1 <- 0.06948962

### (1.2.3) Create "params_surv_list" object by combining the baseline hazard 
### and relative treatment effects
params <- params_surv_list(
  #### Model for PFS
  pfs = params_surv(
    coefs = list( 
      rate = data.frame( # coefficients predict log rate
        intercept = rnorm(N_SAMPLES, logint_pfs_est, logint_pfs_se),
        new1 = rnorm(N_SAMPLES, loghr_pfs_est_new1, loghr_pfs_se_new1)
      )
    ),
    dist = "exp"
  ),
  
  #### Model for OS
  os = params_surv(
    coefs = list(
      rate = data.frame(
        intercept = rnorm(N_SAMPLES, logint_os_est, logint_os_se),
        new1 = rnorm(N_SAMPLES, loghr_os_est_new1, loghr_os_se_new1)
      )
    ),
    dist = "exp"
  )
)

#### The print (and summary) methods for the "params_surv_list" object will 
#### summarize each of the model terms, which is a good way to check
#### if it's been setup correctly
params 

# (2) Simulation
## (2.1) Construct the model
### (2.1.1) Case where patient-level data was available
### Use create_PsmCurves.params_flexsurvreg_list() method
surv_input_data <- expand(hesim_dat, by = c("strategies", "patients"))
psm_curves1 <- create_PsmCurves(fits, input_data = surv_input_data, 
                                n = N_SAMPLES,
                                uncertainty = "normal",
                                est_data = surv_est_data)

### (2.1.2) Case where patient-level data was NOT available
### Use create_PsmCurves.params_surv_list() method
surv_input_data$intercept <- 1
surv_input_data$new1 <- ifelse(surv_input_data$strategy_name == "New 1", 
                               1, 0)
psm_curves2 <- create_PsmCurves(params, input_data = surv_input_data)

## (2.2) Summarize survival models
## There are minor discrepancies between the case where models were fit
## with flexsurvreg() and the case where the "params_surv_list" object
## was constructed manually due to differences in the random draws
## of the parameter samples. These differences are decreasing in the size 
## of N_SAMPLES
times <- seq(0, 10, 1/12) # Monthly times

### Quantiles
head(psm_curves1$quantile(p = c(.25, .5, .75)))
head(psm_curves2$quantile(p = c(.25, .5, .75)))

### Survival curves
head(psm_curves1$survival(t = times))
head(psm_curves2$survival(t = times))

### Restricted mean survival
head(psm_curves1$rmst(t = c(2, 5)))
head(psm_curves2$rmst(t = c(2, 5)))

Model for state values

Description

Simulate values (i.e., utility or costs) associated with health states in a state transition or partitioned survival model.

Public fields

Methods

Public methods

• StateVals$new()

• StateVals$sim()

• StateVals$check()

• StateVals$clone()

Method new()

Create a new StateVals object.

Usage

StateVals$new(
  params,
  input_data = NULL,
  method = c("wlos", "starting"),
  time_reset = FALSE
)

Arguments

Returns

A new StateVals object.

Method sim()

Simulate state values with either predicted means or random samples by treatment strategy, patient, health state, and time t.

Usage

StateVals$sim(t, type = c("predict", "random"))

Arguments

Returns

A data.table of simulated state values with columns for sample, strategy_id, patient_id, state_id, time, and value.

Method check()

Input validation for class. Checks that fields are the correct type.

Usage

StateVals$check()

Method clone()

The objects of this class are cloneable with this method.

Usage

StateVals$clone(deep = FALSE)

Arguments

Examples

# Simple sick-sicker example where drug costs vary by treatment strategy
# and over time. Prior to time = 5, costs are $10,000 for treatment strategy 
# 1 and $5,000 for treatment strategy 2. After time = 5, costs are $2,000
# for both treatment strategies

## Setup the model
hesim_dat <- hesim_data(
  strategies = data.frame(strategy_id = c(1, 2)),
  patients = data.frame(patient_id = 1:3),
  states = data.frame(state_id = c(1, 2), # Non-death states
                      state_name = c("sick", "sicker")) 
)

## Drug costs vary by health state and time interval
drugcost_tbl <- stateval_tbl(
  data.frame(
    strategy_id = c(1, 1, 2, 2),
    time_start = c(0, 5, 0, 5),
    est = c(10000, 2000, 5000, 2000)
  ),
  dist = "fixed"
)
drugcost_tbl

## Create drug cost model
drugcostmod <- create_StateVals(drugcost_tbl, n = 1, hesim_data = hesim_dat)
      
## Explore predictions from the drug cost model
drugcostmod$sim(t = c(2, 6), type = "predict")
 

Absorbing states

Description

This is a generic function that returns a vector of absorbing states.

Usage

absorbing(x, ...)

## S3 method for class 'matrix'
absorbing(x, ...)

## S3 method for class 'tparams_transprobs'
absorbing(x, ...)

Arguments

Apply relative risks to transition probability matrices

Description

Elements of transition probability matrices are multiplied by relative risks and the transition probability matrices are adjusted so that rows sum to 1. Operations are vectorized and each relative risk is multiplied by every transition matrix (stored in 3-dimensional arrays).

Usage

apply_rr(x, rr, index, complement = NULL)

Arguments

Details

This function is useful for applying relative treatment effects measured using relative risks to an existing transition probability matrix. For example, a transition probability matrix for the reference treatment strategy may exist or have been estimated from the data. Relative risks estimated from a meta-analysis or network meta-analysis can then be applied to the reference transition probability matrix. If the number of rows in rr exceeds x, then the arrays in x are recycled to the number of rows in rr, which facilitates the application of relative risks from multiple treatment strategies to a reference treatment.

Value

A 3-dimensional array where each slice contains matrices of the same dimension as each matrix in x and the number of slices is equal to the number of rows in rr.

Examples

p_12 <- c(.7, .5)
p_23 <- c(.1, .2)
x <- as_array3(tpmatrix(
  C, p_12, .1,
  0, C,     p_23,
  0, 0,     1
))

# There are the same number of relative risk rows and transition probability matrices
rr_12 <- runif(2, .8, 1)
rr_13 <- runif(2, .9, 1)
rr <- cbind(rr_12, rr_13)
apply_rr(x, rr, 
         index = list(c(1, 2), c(1, 3)),
         complement = list(c(1, 1), c(2, 2)))
         
# There are more relative risk rows than transition probability matrices
rr_12 <- runif(4, .8, 1)
rr_13 <- runif(4, .9, 1)
rr <- cbind(rr_12, rr_13)
apply_rr(x, rr, 
         index = list(c(1, 2), c(1, 3)),
         complement = list(c(1, 1), c(2, 2)))

Coerce to data.table

Description

Creates a data.table that combines the transition probability matrices and ID variables from a tparams_transprobs object. This is often useful for debugging.

Usage

## S3 method for class 'tparams_transprobs'
as.data.table(x, ..., prefix = "prob_", sep = "_", long = FALSE)

Arguments

Value

The output always contains columns for the ID variables and the transition probabilities, but the form depends on on the long argument. If FALSE, then a data.table with one row for each transition probability matrix is returned; otherwise, the data.table contains one row for each transition and columns from (the state being transitioned from) and to (the state being transitioned to) are added.

See Also

tparams_transprobs()

Examples

# Create tparams_transprobs object
hesim_dat <- hesim_data(strategies = data.frame(strategy_id = 1:2),
                        patients = data.frame(patient_id = 1:3))
input_data <- expand(hesim_dat, by = c("strategies", "patients"))    
tpmat_id <- tpmatrix_id(input_data, n_samples = 2)      
p_12 <- runif(nrow(tpmat_id), .6, .7) + 
  .05 * (tpmat_id$strategy_id == 2)
tpmat <- tpmatrix(
  C, p_12,
  0, 1
)
tprobs <- tparams_transprobs(tpmat, tpmat_id)

# Convert to data.table in "wide" format
as.data.table(tprobs)
as.data.table(tprobs, prefix = "")
as.data.table(tprobs, prefix = "", sep = ".")

# Convert to data.table in "long: format
as.data.table(tprobs, long = TRUE)

Convert between 2D tabular objects and 3D arrays

Description

Convert a 2-dimensional tabular object where each row stores a flattened square matrix to a 3-dimensional array of square matrices and vice versa. This allows multiple transition matrices to be stored as either tabular objects (e.g., matrices, data frames, etc) or as arrays.

Usage

as_array3(x)

as_tbl2(
  x,
  output = c("data.table", "data.frame", "matrix", "tpmatrix"),
  prefix = "",
  sep = "_"
)

Arguments

Value

For as_array3() a 3-dimensional array of square matrices; for as_tbl2() a 2-dimensional tabular object as specified by output.

See Also

tpmatrix

Examples

p_12 <- c(.7, .6)
pmat <- tpmatrix(
 C, p_12,
 0, 1
)
pmat

as_array3(pmat)
as_array3(as.matrix(pmat))
as_tbl2(as_array3(pmat))
as_tbl2(as_array3(pmat), prefix = "p_", sep = ".")

Convert multi-state data to PFS and OS data

Description

Convert a multi-state dataset with irreversible transitions containing 3 health states to a dataset with one row per patient and progression-free survival (PFS) and overall survival (OS) time-to-event outcomes.

Usage

as_pfs_os(
  data,
  patient_vars,
  status = "status",
  time_stop = "time_stop",
  transition = "transition_id"
)

Arguments

Value

A data.table with one row per patient containing each variable in patient_vars as well as a time variable and status indicator for both PFS (pfs_status, pfs_time) and OS (os_time, os_status).

Examples

as_pfs_os(onc3, patient_vars = c("patient_id", "strategy_name", "female", "age")) 

Plot state probabilities

Description

Quickly plot state probabilities stored in a stateprobs object.

Usage

## S3 method for class 'stateprobs'
autoplot(
  object,
  labels = NULL,
  ci = FALSE,
  prob = 0.95,
  ci_style = c("ribbon", "line"),
  geom_alpha = 0.3,
  ...
)

Arguments

Value

A ggplot object.

Note

If there are multiple patients/groups, then state probabilities are averaged across patients/groups (using the weights in patient_wt if available) prior to plotting.

See Also

Psm for an example.

Plot survival curves

Description

Quickly plot survival curves stored in a survival object.

Usage

## S3 method for class 'survival'
autoplot(
  object,
  labels = NULL,
  ci = FALSE,
  prob = 0.95,
  ci_style = c("ribbon", "line"),
  geom_alpha = 0.3,
  ...
)

Arguments

Value

A ggplot object.

Note

If there are multiple patients, then survival probabilities are averaged across patients (using the weights in patient_wt if available) prior to plotting.

See Also

Psm for an example.

Bootstrap a statistical model

Description

bootstrap is a generic function for generating bootstrap replicates of the parameters of a fitted statistical model.

Usage

bootstrap(object, B, ...)

## S3 method for class 'partsurvfit'
bootstrap(object, B, max_errors = 0, silent = FALSE, ...)

Arguments

Value

Sampled values of the parameters.

A cost-effectiveness object

Description

An object that summarizes simulated measures of clinical effectiveness and costs from a simulation model for use in a cost-effectiveness analysis.

Format

A list containing two elements:

costs

Total (discounted) costs by category.

qalys

(Discounted) quality-adjusted life-years.

Costs

The costs data.table contains the following columns:

category

The cost category.

dr

The discount rate.

sample

A randomly sampled parameter set from the probabilistic sensitivity analysis (PSA)

strategy_id

The treatment strategy ID.

grp_id

An optional column denoting a subgroup. If not included, it is assumed that a single subgroup is being analyzed.

costs

Costs.

Quality-adjusted life-years

The qalys data.table contains the following columns:

dr

The discount rate.

sample

A randomly sampled parameter set from the probabilistic sensitivity analysis (PSA)

strategy_id

The treatment strategy ID.

grp_id

An optional column denoting a subgroup. If not included, it is assumed that a single subgroup is being analyzed.

qalys

Quality-adjusted life-years

Cost-effectiveness analysis

Description

Conduct cost-effectiveness analysis (CEA) given output of an economic model; that is, summarize a probabilistic sensitivity analysis (PSA), possibly by subgroup.

• cea() computes the probability that each treatment is most cost-effective, output for a cost-effectiveness acceptability frontier, the expected value of perfect information, and the net monetary benefit for each treatment.

• cea_pw() conducts pairwise CEA by comparing strategies to a comparator. Computed quantities include the incremental cost-effectiveness ratio, the incremental net monetary benefit, output for a cost-effectiveness plane, and output for a cost-effectiveness acceptability curve.

Usage

cea(x, ...)

cea_pw(x, ...)

## Default S3 method:
cea(x, k = seq(0, 2e+05, 500), sample, strategy, grp = NULL, e, c, ...)

## Default S3 method:
cea_pw(
  x,
  k = seq(0, 2e+05, 500),
  comparator,
  sample,
  strategy,
  grp = NULL,
  e,
  c,
  ...
)

## S3 method for class 'ce'
cea(x, k = seq(0, 2e+05, 500), dr_qalys, dr_costs, ...)

## S3 method for class 'ce'
cea_pw(x, k = seq(0, 2e+05, 500), comparator, dr_qalys, dr_costs, ...)

Arguments

Value

cea() returns a list of four data.table elements.

summary

A data.table of the mean, 2.5% quantile, and 97.5% quantile by strategy and group for clinical effectiveness and costs.

mce

The probability that each strategy is the most effective treatment for each group for the range of specified willingness to pay values. In addition, the column best denotes the optimal strategy (i.e., the strategy with the highest expected net monetary benefit), which can be used to plot the cost-effectiveness acceptability frontier (CEAF).

evpi

The expected value of perfect information (EVPI) by group for the range of specified willingness to pay values. The EVPI is computed by subtracting the expected net monetary benefit given current information (i.e., the strategy with the highest expected net monetary benefit) from the expected net monetary benefit given perfect information.

nmb

The mean, 2.5% quantile, and 97.5% quantile of net monetary benefits for the range of specified willingness to pay values.

cea_pw also returns a list of four data.table elements:

summary

A data.table of the mean, 2.5% quantile, and 97.5% quantile by strategy and group for incremental clinical effectiveness and costs.

delta

Incremental effectiveness and incremental cost for each simulated parameter set by strategy and group. Can be used to plot a cost-effectiveness plane.

ceac

Values needed to plot a cost-effectiveness acceptability curve by group. The CEAC plots the probability that each strategy is more cost-effective than the comparator for the specified willingness to pay values.

inmb

The mean, 2.5% quantile, and 97.5% quantile of incremental net monetary benefits for the range of specified willingness to pay values.

Examples

library("data.table")
library("ggplot2")
theme_set(theme_bw())

# Simulation output
n_samples <- 30

sim <- data.table(sample = rep(seq(n_samples), 4),
                  c = c(rlnorm(n_samples, 5, .1), rlnorm(n_samples, 5, .1),
                        rlnorm(n_samples, 11, .1), rlnorm(n_samples, 11, .1)),
                  e = c(rnorm(n_samples, 8, .2), rnorm(n_samples, 8.5, .1),
                        rnorm(n_samples, 11, .6), rnorm(n_samples, 11.5, .6)),
                  strategy_id = rep(1:2, each = n_samples * 2),
                  grp_id = rep(rep(1:2, each = n_samples), 2)
)

# Cost-effectiveness analysis
cea_out <- cea(sim, k = seq(0, 200000, 500), sample = "sample", 
               strategy = "strategy_id", grp = "grp_id", 
               e = "e", c = "c")
names(cea_out)

## Some sample output
## The probability that each strategy is the most cost-effective 
## in each group with a willingness to pay of 20,000
cea_out$mce[k == 20000]

# Pairwise cost-effectiveness analysis
cea_pw_out <-  cea_pw(sim,  k = seq(0, 200000, 500), comparator = 1,
                      sample = "sample", strategy = "strategy_id", 
                      grp = "grp_id", e = "e", c = "c")
names(cea_pw_out)

## Some sample output
## The cost-effectiveness acceptability curve
head(cea_pw_out$ceac[k >= 20000])

# Summarize the incremental cost-effectiveness ratio
labs <- list(strategy_id = c("Strategy 1" = 1, "Strategy 2" = 2),
             grp_id = c("Group 1" = 1, "Group 2" = 2))
format(icer(cea_pw_out, labels = labs))

# Plots
plot_ceplane(cea_pw_out, label = labs)
plot_ceac(cea_out, label = labs)
plot_ceac(cea_pw_out, label = labs)
plot_ceaf(cea_out, label = labs)
plot_evpi(cea_out, label = labs)

Input validation for class objects

Description

check is a generic function for validating the inputs of class objects.

Usage

## S3 method for class 'id_attributes'
check(object, ...)

## S3 method for class 'input_mats'
check(object, ...)

## S3 method for class 'params_lm'
check(object, ...)

## S3 method for class 'params_mlogit'
check(object, ...)

## S3 method for class 'params_surv'
check(object, ...)

## S3 method for class 'params_surv_list'
check(object, ...)

## S3 method for class 'tparams_mean'
check(object, ...)

## S3 method for class 'tparams_transprobs'
check(object, ...)

check(object, ...)

Arguments

Value

If validation is successful, returns the object in question; otherwise, informs the user that an error has occurred.

Check input data argument for create_input_mats

Description

Check that input data argument for create_input_mats exists and that it is of the correct type.

Usage

check_input_data(input_data)

Arguments

Value

If all tests passed, returns nothing; otherwise, throws an exception.

Costs object

Description

An object of class costs returned from methods ⁠$sim_costs()⁠ in model classes that store simulated costs.

Components

A costs object inherits from data.table and contains the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

grp_id

The subgroup ID.

state_id

The health state ID.

dr

The rate used to discount costs.

category

The cost category (e.g., drug costs, medical costs, etc).

costs

The simulated cost values.

Create CohortDtstm object

Description

A generic function for creating an object of class CohortDtstm.

Usage

create_CohortDtstm(object, ...)

## S3 method for class 'model_def'
create_CohortDtstm(
  object,
  input_data,
  cost_args = NULL,
  utility_args = NULL,
  ...
)

Arguments

Create CohortDtstmTrans object

Description

A generic function for creating an object of class CohortDtstmTrans.

Usage

create_CohortDtstmTrans(object, ...)

## S3 method for class 'multinom_list'
create_CohortDtstmTrans(
  object,
  input_data,
  trans_mat,
  n = 1000,
  uncertainty = c("normal", "none"),
  ...
)

## S3 method for class 'msm'
create_CohortDtstmTrans(
  object,
  input_data,
  cycle_length,
  n = 1000,
  uncertainty = c("normal", "none"),
  ...
)

## S3 method for class 'params_mlogit_list'
create_CohortDtstmTrans(object, input_data, trans_mat, ...)

Arguments

Details

Disease models may either be created from a fitted statistical model or from a parameter object. In the case of the former, input_data is a data frame like object that is used to look for variables from the statistical model that are required for simulation. In this sense, input_data is very similar to the newdata argument in most predict() methods (e.g., see predict.lm()). In other words, variables used in the formula of the statistical model must also be in input_data.

In the case of the latter, the columns of input_data must be named in a manner that is consistent with the parameter object. In the typical case (e.g., with params_surv or params_mlogit), the parameter object contains coefficients from a regression model, usually stored as matrix where rows index parameter samples (i.e., for a probabilistic sensitivity analysis) and columns index model terms. In such instances, there must be one column from input_data with the same name as each model term in the coefficient matrix; that is, the columns in input_data are matched with the columns of the coefficient matrices by name. If there are model terms in the coefficient matrices that are not contained in input_data, then an error will be thrown.

See Also

See CohortDtstmTrans for examples.

Create IndivCtstmTrans object

Description

A generic function for creating an object of class IndivCtstmTrans.

Usage

create_IndivCtstmTrans(object, ...)

## S3 method for class 'flexsurvreg_list'
create_IndivCtstmTrans(
  object,
  input_data,
  trans_mat,
  clock = c("reset", "forward"),
  n = 1000,
  uncertainty = c("normal", "none"),
  ...
)

## S3 method for class 'flexsurvreg'
create_IndivCtstmTrans(
  object,
  input_data,
  trans_mat,
  clock = c("reset", "forward"),
  n = 1000,
  uncertainty = c("normal", "none"),
  ...
)

## S3 method for class 'params_surv'
create_IndivCtstmTrans(
  object,
  input_data,
  trans_mat,
  clock = c("reset", "forward", "mix", "mixt"),
  reset_states = NULL,
  transition_types = NULL,
  ...
)

## S3 method for class 'params_surv_list'
create_IndivCtstmTrans(
  object,
  input_data,
  trans_mat,
  clock = c("reset", "forward", "mix", "mixt"),
  reset_states = NULL,
  transition_types = NULL,
  ...
)

Arguments

Details

Disease models may either be created from a fitted statistical model or from a parameter object. In the case of the former, input_data is a data frame like object that is used to look for variables from the statistical model that are required for simulation. In this sense, input_data is very similar to the newdata argument in most predict() methods (e.g., see predict.lm()). In other words, variables used in the formula of the statistical model must also be in input_data.

In the case of the latter, the columns of input_data must be named in a manner that is consistent with the parameter object. In the typical case (e.g., with params_surv or params_mlogit), the parameter object contains coefficients from a regression model, usually stored as matrix where rows index parameter samples (i.e., for a probabilistic sensitivity analysis) and columns index model terms. In such instances, there must be one column from input_data with the same name as each model term in the coefficient matrix; that is, the columns in input_data are matched with the columns of the coefficient matrices by name. If there are model terms in the coefficient matrices that are not contained in input_data, then an error will be thrown.

Value

Returns an R6::R6Class object of class IndivCtstmTrans.

See Also

See IndivCtstmTrans and IndivCtstm for examples.

Create PsmCurves object

Description

A generic function for creating a PsmCurves object.

Usage

create_PsmCurves(object, ...)

## S3 method for class 'flexsurvreg_list'
create_PsmCurves(
  object,
  input_data,
  n = 1000,
  uncertainty = c("normal", "bootstrap", "none"),
  est_data = NULL,
  ...
)

## S3 method for class 'params_surv_list'
create_PsmCurves(object, input_data, ...)

Arguments

Details

Disease models may either be created from a fitted statistical model or from a parameter object. In the case of the former, input_data is a data frame like object that is used to look for variables from the statistical model that are required for simulation. In this sense, input_data is very similar to the newdata argument in most predict() methods (e.g., see predict.lm()). In other words, variables used in the formula of the statistical model must also be in input_data.

In the case of the latter, the columns of input_data must be named in a manner that is consistent with the parameter object. In the typical case (e.g., with params_surv or params_mlogit), the parameter object contains coefficients from a regression model, usually stored as matrix where rows index parameter samples (i.e., for a probabilistic sensitivity analysis) and columns index model terms. In such instances, there must be one column from input_data with the same name as each model term in the coefficient matrix; that is, the columns in input_data are matched with the columns of the coefficient matrices by name. If there are model terms in the coefficient matrices that are not contained in input_data, then an error will be thrown.

Value

Returns an R6Class object of class PsmCurves.

See Also

See PsmCurves and Psm for examples. PsmCurves provides an example in which a model is parameterized both with (via create_PsmCurves.flexsurvreg_list()) and without (via create_PsmCurves.params_surv_list()) access to patient-level data. The Psm example shows how state probabilities, costs, and utilities can be computed from predicted survival curves.

Create a StateVals object

Description

create_StateVals() is a generic function for creating an object of class StateVals from a fitted statistical model or a stateval_tbl object.

Usage

create_StateVals(object, ...)

## S3 method for class 'lm'
create_StateVals(
  object,
  input_data = NULL,
  n = 1000,
  uncertainty = c("normal", "none"),
  ...
)

## S3 method for class 'stateval_tbl'
create_StateVals(object, hesim_data = NULL, n = 1000, ...)

Arguments

Details

If object is a stateval_tbl, then a hesim_data object is used to specify treatment strategies, patients, and/or health states not included as columns in the table, or, to match patients in the table to groups. Not required if the table includes one row for each treatment strategy, patient, and health state combination. Patients are matched to groups by specifying both a patient_id and a grp_var column in the patients table.

Value

A StateVals object.

See Also

See StateVals for documentation of the class and additional examples. An example use case for create_StateVals.stateval_tbl() is provided in the stateval_tbl() documentation.

Examples

set.seed(10)

# EXAMPLE FOR `create_statevals.lm()`
## Simple example comparing two treatment strategies where
## medical costs vary by sex and health state

## Setup model
hesim_dat <- hesim_data(
  strategies = data.frame(strategy_id = c(1, 2)),
  patients = data.frame(
    patient_id = c(1, 2),
    female = c(1, 0)
  ),
  states = data.frame(
    state_id = c(1, 2, 3),
    state_name = c("state1", "state2", "state3")
  )
)

## Fit model
medcost_estimation_data <- psm4_exdata$costs$medical
medcost_estimation_data$time5 <- rbinom(nrow(medcost_estimation_data), 
                                        1, .5) # Illustrative time dummy
medcost_fit <- lm(costs ~ female + state_name + time5, 
                  data = medcost_estimation_data)

## Create medical cost model
### Allow medical costs to vary across time in addition to by patient and 
### health state
medcost_times <- time_intervals(
  data.frame(time_start = c(0, 3, 5),
            time5 = c(0, 0, 1)) # Time dummy corresponds to time > 5
)
medcost_input_data <- expand(hesim_dat, 
                             by = c("strategies", "patients", "states"),
                             times = medcost_times)
medcost_model <- create_StateVals(medcost_fit, medcost_input_data,
                                  n = 1)

## Explore predictions from medical cost model
### We can assess predictions at multiple time points
medcost_model$sim(t = c(1, 6), type = "predict")

Create input matrices

Description

create_input_mats() is a generic function for creating an object of class input_mats. Model matrices are constructed based on the variables specified in the model object and the data specified in input_data. create_input_mats() is not typically called by users directly, but is instead used by functions that create model objects (e.g., create_IndivCtstmTrans(), create_CohortDtstmTrans(), create_PsmCurves()).

Usage

create_input_mats(object, ...)

## S3 method for class 'lm'
create_input_mats(object, input_data, ...)

## S3 method for class 'flexsurvreg'
create_input_mats(object, input_data, ...)

## S3 method for class 'flexsurvreg_list'
create_input_mats(object, input_data, ...)

## S3 method for class 'partsurvfit'
create_input_mats(object, input_data, ...)

## S3 method for class 'params_lm'
create_input_mats(object, input_data, ...)

## S3 method for class 'params_surv'
create_input_mats(object, input_data, ...)

## S3 method for class 'params_surv_list'
create_input_mats(object, input_data, ...)

## S3 method for class 'multinom'
create_input_mats(object, input_data, ...)

## S3 method for class 'multinom_list'
create_input_mats(object, input_data, ...)

## S3 method for class 'params_mlogit_list'
create_input_mats(object, input_data, ...)

Arguments

Value

An object of class input_mats.

See Also

input_mats()

Examples

library("flexsurv")

strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3),
                       age = c(45, 47, 60),
                       female = c(1, 0, 0),
                       group = factor(c("Good", "Medium", "Poor")))
states <- data.frame(state_id =  seq(1, 3),
                     state_name = factor(paste0("state", seq(1, 3))))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)

# Class "lm"
input_data <- expand(hesim_dat, by = c("strategies", "patients", "states"))
medcost_fit <- lm(costs ~ female + state_name, psm4_exdata$costs$medical)
input_mats <- create_input_mats(medcost_fit, input_data)
input_mats

# Class "flexsurvreg"
input_data <- expand(hesim_dat, by = c("strategies", "patients"))
fit_wei <- flexsurvreg(formula = Surv(futime, fustat) ~ 1,
                       data = ovarian, dist = "weibull")
input_mats <- create_input_mats(fit_wei, input_data)
input_mats

Create input matrices from formula

Description

This is an internal function for creating input matrices from formulas. It is currently used in some unit tests.

Usage

## S3 method for class 'formula_list'
create_input_mats(object, input_data, ...)

Arguments

Value

An object of class input_mats.

See Also

create_input_mats()

Create a data table of treatment lines

Description

Convert a list of treatment lines for multiple treatment strategies to a data.table.

Usage

create_lines_dt(strategy_list, strategy_ids = NULL)

Arguments

Value

Returns a data.table in tidy format with three columns:

strategy_id

Treatment strategy ids.

line

Line of therapy.

treatment_id

Treatment ID for treatment used at a given line of therapy within a treatment strategy.

Examples

strategies <- list(c(1, 2, 3),
                  c(1, 2))
create_lines_dt(strategies)

Form a list from ...

Description

Form a list of objects from ....

Usage

create_object_list(...)

Arguments

Value

A list of objects from ....

Create a parameter object from a fitted model

Description

create_params is a generic function for creating an object containing parameters from a fitted statistical model. If uncertainty != "none", then random samples from suitable probability distributions are returned.

Usage

create_params(object, ...)

## S3 method for class 'lm'
create_params(object, n = 1000, uncertainty = c("normal", "none"), ...)

## S3 method for class 'multinom'
create_params(object, n = 1000, uncertainty = c("normal", "none"), ...)

## S3 method for class 'multinom_list'
create_params(object, n = 1000, uncertainty = c("normal", "none"), ...)

## S3 method for class 'flexsurvreg'
create_params(object, n = 1000, uncertainty = c("normal", "none"), ...)

## S3 method for class 'flexsurvreg_list'
create_params(object, n = 1000, uncertainty = c("normal", "none"), ...)

## S3 method for class 'partsurvfit'
create_params(
  object,
  n = 1000,
  uncertainty = c("normal", "bootstrap", "none"),
  max_errors = 0,
  silent = FALSE,
  ...
)

Arguments

Value

An object prefixed by params_. Mapping between create_params and the classes of the returned objects are:

• create_params.lm -> params_lm

• create_params.multinom -> params_mlogit

• create_params.multinom_list -> params_mlogit_list

• create_params.flexsurvreg -> params_surv

• create_params.flexsurvreg_list -> params_surv_list

• create_params.partsurvfit -> params_surv_list

See Also

These methods are typically used alongside create_input_mats() to create model objects as a function of input data and a fitted statistical model. For instance, create_PsmCurves() creates the survival model for a partitioned survival model, create_IndivCtstmTrans() creates the transition model for an individual continuous time state transition model, create_CohortDtstmTrans() creates the transition model for a cohort discrete time state transition model, and create_StateVals() creates a health state values model.

Examples

# create_params.lm
fit <- lm(costs ~ female, data = psm4_exdata$costs$medical)
n <- 5
params_lm <- create_params(fit, n = n)
head(params_lm$coefs)
head(params_lm$sigma)

# create_params.flexsurvreg
library("flexsurv")
fit <- flexsurvreg(formula = Surv(futime, fustat) ~ 1, 
                   data = ovarian, dist = "weibull")
n <- 5
params_surv_wei <- create_params(fit, n = n)
print(params_surv_wei$dist)
head(params_surv_wei$coefs)

Create a data table of health state transitions

Description

Create a data table of health state transitions from a transition matrix describing the states and transitions in a multi-state model suitable for use with hesim_data.

Usage

create_trans_dt(trans_mat)

Arguments

Value

Returns a data.table::data.table in tidy format with three columns:

transition_id

Health state transition ID.

from

The starting health state.

to

The health state that will be transitions to.

Examples

tmat <- rbind(c(NA, 1, 2),
              c(NA, NA, 3),
              c(NA, NA, NA))
create_trans_dt(tmat)

Define and evaluate model expression

Description

A model expression is defined by specifying random number generation functions for a probabilistic sensitivity analysis (PSA) and transformations of the sampled parameters as a function of input_data. The unevaluated expressions are evaluated with eval_model() and used to generate the model inputs needed to create an economic model.

Usage

define_model(tparams_def, rng_def, params = NULL, n_states = NULL)

eval_model(x, input_data)

Arguments

Details

eval_model() evaluates the expressions in an object of class model_def returned by define_model() and is, in turn, used within functions that instantiate economic models (e.g., create_CohortDtstm()). The direct output of eval_model() can also be useful for understanding and debugging model definitions, but it is not used directly for simulation.

Economic models are constructed as a function of input data and parameters:

1. Input data: Objects of class expanded_hesim_data consisting of the treatment strategies and patient population.

2. Parameters: The underlying parameter estimates from the literature are first stored in a list (params argument). Random number generation is then used to sample the parameters from suitable probability distributions for the PSA (rng_def argument). Finally, the sampled parameters are transformed as a function of the input data into values (e.g., elements of a transition probability matrix) used for the simulation (tparams_def argument). The params argument can be omitted if the underlying parameters values are defined inside a define_rng() block.

Value

define_model() returns an object of class model_def, which is a list containing the arguments to the function. eval_model() returns a list containing ID variables identifying parameter samples, treatment strategies, patient cohorts, and time intervals; the values of parameters of the transition probability matrix, utilities, and/or cost categories; the number of health states; and the number of random number generation samples for the PSA.

See Also

define_tparams(), define_rng()

Examples

# Data
library("data.table")
strategies <- data.table(strategy_id = 1:2,
                         strategy_name = c("Monotherapy", "Combination therapy"))
patients <- data.table(patient_id = 1)
hesim_dat <- hesim_data(strategies = strategies,
                       patients = patients)
data <- expand(hesim_dat)

# Model parameters
rng_def <- define_rng({
  alpha <- matrix(c(1251, 350, 116, 17,
                    0, 731, 512, 15,
                    0, 0, 1312, 437,
                    0, 0, 0, 469),
                  nrow = 4, byrow = TRUE)
  rownames(alpha) <- colnames(alpha) <- c("A", "B", "C", "D")
  lrr_mean <- log(.509)
  lrr_se <- (log(.710) - log(.365))/(2 * qnorm(.975))
  
  list(
    p_mono = dirichlet_rng(alpha),
    rr_comb = lognormal_rng(lrr_mean, lrr_se),
    u = 1,
    c_zido = 2278,
    c_lam = 2086.50,
    c_med = gamma_rng(mean = c(A = 2756, B = 3052, C = 9007),
                      sd = c(A = 2756, B = 3052, C = 9007))
  )
}, n = 2)

tparams_def <- define_tparams({
  rr = ifelse(strategy_name == "Monotherapy", 1, rr_comb)
  list(
    tpmatrix = tpmatrix(
      C, p_mono$A_B * rr, p_mono$A_C * rr, p_mono$A_D * rr,
      0, C, p_mono$B_C * rr, p_mono$B_D * rr,
      0, 0, C, p_mono$C_D * rr,
      0, 0, 0, 1),
    utility = u,
    costs = list(
      drug = ifelse(strategy_name == "Monotherapy",
                    c_zido, c_zido + c_lam),
      medical = c_med
    ) 
  )
})

# Simulation
## Define the economic model
model_def <- define_model(
  tparams_def = tparams_def,
  rng_def = rng_def)

### Evaluate the model expression to generate model inputs
### This can be useful for understanding the output of a model expression
eval_model(model_def, data)

## Create an economic model with a factory function
econmod <- create_CohortDtstm(model_def, data)

Define and evaluate random number generation expressions

Description

Random number generation expressions are used to randomly sample model parameters from suitable distributions for probabilistic sensitivity analysis. These functions are typically used when evaluating an object of class model_def defined using define_model().

Usage

define_rng(expr, n = 1, ...)

eval_rng(x, params = NULL, check = TRUE)

Arguments

Details

hesim contains a number of random number generation functions that return parameter samples in convenient formats and do not typically require the number of samples, n, as arguments (see rng_distributions). The random number generation expressions are evaluated using eval_rng() and used within expr in define_rng(). If a multivariate object is returned by eval_rng(), then the rows are random samples and columns are distinct parameters (e.g., costs for each health state, elements of a transition probability matrix).

Value

define_rng() returns an object of class rng_def, which is a list containing the unevaluated random number generation expressions passed to expr, n, and any additional arguments passed to ... . eval_rng() evaluates the rng_def object and returns an eval_rng object containing the evaluated expression.

See Also

Parameters can be conveniently sampled from probability distributions using a number of random number generation functions (see rng_distributions). An economic model can be created with create_CohortDtstm() by using define_rng() (or a previously evaluated eval_rng object) alongside define_tparams() to define a model with define_model(). It can be useful to summarize an evaluated expression with summary.eval_rng().

Examples

 
params <- list(
  alpha = matrix(c(75, 25, 33, 67), byrow = TRUE, ncol = 2),
  inptcost_mean = c(A = 900, B = 1500, C = 2000),
  outptcost_mean = matrix(c(300, 600, 800,
                            400, 700, 700),
                           ncol = 3, byrow = TRUE)
)
rng_def <- define_rng({
  aecost_mean <- c(500, 800, 1000) # Local object not 
                                   # not returned by eval_rng()
  list( # Sampled values of parameters returned by eval_rng()
    p = dirichlet_rng(alpha), # Default column names
    inptcost = gamma_rng(mean = inptcost_mean, # Column names based on 
                         sd = inptcost_mean),  # named vector
    outptcost = outptcost_mean, # No column names because
                                # outptcost_mean has none.
    aecost = gamma_rng(mean = aecost_mean, # Explicit naming of columns
                       sd = aecost_mean,
                       names = aecost_colnames)
  )
}, n = 2, aecost_colnames = c("A", "B", "C")) # Add aecost_colnames to environment
params_sample <- eval_rng(x = rng_def, params)
summary(params_sample)
params_sample

Define and evaluate transformed parameter expressions

Description

Transformed parameter expressions are used to transform the parameter values sampled with eval_rng() as a function of input data (treatment strategies and patients) and time intervals. These functions are used when evaluating an object of class model_def defined using define_model(). The transformed parameters are ultimately converted into tparams objects and used to simulate outcomes with an economic model.

Usage

define_tparams(expr, times = NULL, ...)

eval_tparams(x, input_data, rng_params)

Arguments

Details

define_tparams() is evaluated when creating economic models as a function of model_def objects defined with define_model(). Operations are "vectorized" in the sense that they are performed for each unique combination of input_data and params. expr is evaluated in an environment including each variable from input_data, all elements of rng_params, and a variable time containing the values from times. The time variable can be used to create models where parameters vary as a function of time. eval_tparams() is not exported and is only meant for use within eval_model().

Value

define_tparams() returns an object of class tparams_def, which is a list containing the unevaluated "transformation" expressions passed to expr, times, and any additional arguments passed to ... . eval_tparams() evaluates the tparams_def object and should return a list of transformed parameter objects.

See Also

define_model(), define_rng()

Disease progression object

Description

An object of class disprog returned from methods ⁠$sim_disease()⁠ in model classes. It contains simulated trajectories through a multi-state model.

Components

A disprog object inherits from data.table and contains the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

from

The health state ID transitioned from.

to

The health state ID transitioned to.

final

An indicator equal to 1 if a patient is in their final health state during the simulation and 0 otherwise.

time_start

The time at the start of the interval.

time_stop

The time at the end of the interval.

The object also contains size and absorbing attributes. The size attribute is a numeric vector with the elements n_samples, n_strategies, n_patients, and n_states denoting the number of samples, treatment strategies, patients, and health states The absorbing attribute is a numeric vector containing the absorbing health states; i.e., the health states that cannot be transitioned from. Operationally, an absorbing state is a row in a transition matrix (as in the trans_mat field of the IndivCtstmTrans class) with all NAs.

See Also

A disease progression object can be simulated with either the IndivCtstm or IndivCtstmTrans classes.

Expand object

Description

A generic function for "expanding" an object. Only used for hesim_data objects with expand.hesim_data().

Usage

expand(object, by, times)

See Also

expand.hesim_data()

Expand hesim_data

Description

Create a data table in long format from all combinations of specified tables from an object of class hesim_data and optionally time intervals. See "Details" for an explanation of how the expansion is done.

Usage

## S3 method for class 'hesim_data'
expand(object, by = c("strategies", "patients"), times = NULL)

Arguments

Details

This function is similar to expand.grid(), but works for data frames or data tables. Specifically, it creates a data.table from all combinations of the supplied tables in object and optionally the start of times intervals in times. The supplied tables are determined using the by argument. The resulting dataset is sorted by prioritizing ID variables as follows: (i) strategy_id, (ii) patient_id, (iii) the health-related ID variable (either state_id or transition_id, and (iv) the time intervals from times.

Value

An object of class expanded_hesim_data, which is a data.table with an "id_vars" attribute containing the names of the ID variables in the data table and, if times is not NULL, a time_intervals object derived from times.

Examples

strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3), age = c(65, 50, 75),
                          gender = c("Female", "Female", "Male"))
states <- data.frame(state_id =  seq(1, 3),
                     state_var = c(2, 1, 9))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)
expand(hesim_dat, by = c("strategies", "patients"))
expand(hesim_dat, by = c("strategies", "patients"),
       times = c(0, 2, 10))

Matrix exponential

Description

This is a wrapper around msm::MatrixExp() that computes the exponential of multiple square matrices.

Usage

expmat(x, t = 1, ...)

Arguments

Details

This function is most useful when exponentiating transition intensity matrices to produce transition probability matrices. To create transition probability matrices for discrete time state transition models with annual cycles, set t=1. An array of matrices is returned which can be used to create the value element of a tparams_transprobs object. See qmatrix() for an example.

Value

Returns an array of exponentiated matrices. If length(t) > 1, then length(t) arrays are returned for each element in x.

See Also

qmatrix.msm(), qmatrix.data.table()

Random generation for generalized gamma distribution

Description

Draw random samples from a generalized gamma distribution using the parameterization from flexsurv. Written in C++ for speed. Equivalent to flexsurv::rgengamma.

Usage

fast_rgengamma(n, mu = 0, sigma = 1, Q)

Arguments

Value

A vector of random samples from the generalized gamma distribution. The length of the sample is determined by n. The numerical arguments other than n are recycled so that the number of samples is equal to n.

Examples

n <- 1000
m <- 2 ; s <- 1.7; q <- 1
ptm <- proc.time()
r1 <- fast_rgengamma(n, mu = m, sigma = s, Q = q)
proc.time() - ptm
ptm <- proc.time()
library("flexsurv")
r2 <- flexsurv::rgengamma(n, mu = m, sigma = s, Q = q)
proc.time() - ptm
summary(r1)
summary(r2)

List of flexsurvreg objects

Description

Combine flexsurvreg objects into a list.

Usage

flexsurvreg_list(...)

Arguments

Value

An object of class flexsurvreg_list.

Examples

 library("flexsurv")
 fit1 <- flexsurv::flexsurvreg(formula = Surv(futime, fustat) ~ 1, data = ovarian, dist = "weibull")
 fit2 <- flexsurv::flexsurvreg(formula = Surv(futime, fustat) ~ 1, data = ovarian, dist = "exp")
 fsreg_list <- flexsurvreg_list(wei = fit1, exp = fit2)
 class(fsreg_list)

List of formula objects

Description

Combine formula or formula_list object into a formula_list object.

Usage

formula_list(...)

Arguments

Value

An object of class formula_list.

Examples

# Create from "formula" objects
flist_wei <- formula_list(shape = formula(~ 1), scale = formula(~ x))
class(flist_wei)

# Create from "formula_list" objects
flist <- formula_list(exponential = formula_list(rate = formula(~1)),
                              weibull = flist_wei)

Get value labels

Description

Get value labels for the ID variables in a hesim_data object and create a list of named vectors that can be passed to formatting and plotting functions. This lets users create nice labels for treatment strategies, subgroups, health states, and/or transitions when presenting results.

Usage

get_labels(
  object,
  strategy = "strategy_name",
  grp = "grp_name",
  state = "state_name",
  transition = "transition_name",
  death_label = "Death"
)

Arguments

Value

A list of named vectors containing the values and labels of variables. The elements of each vector are the values of a variable and the names are the labels. The names of the list are the names of the ID variables.

See Also

hesim_data(), set_labels()

Examples

library("data.table")
strategies <- data.table(
  strategy_id = c(1, 2),
  strategy_name = c("Strategy 1", "Strategy 2")
)
patients <- data.table(
  patient_id = seq(1, 4),
  age = c(50, 55, 60, 65),
  grp_id = c(1, 1, 2, 2),
  grp_name = rep(c("Age 50-59", "Age 60-69"), each = 2)
)
states <- data.table(
  state_id =  seq(1, 2),
  state_name = c("State 1", "State 2")
)
hesim_dat <- hesim_data(
  strategies = strategies,
  patients = patients,
  states = states
)
labs <- get_labels(hesim_dat)
labs

# Pass to set_labels()
d <- data.table(strategy_id = c(1, 1, 2, 2),
                grp_id = c(1, 2, 1, 2))
set_labels(d, labs, new_name = c("strategy_name", "grp_name"))
d

Data for health economic simulation modeling

Description

A list of tables required for health economic simulation modeling. This object is used to setup models by defining the treatment strategies, target population, and model structure.

Usage

hesim_data(strategies, patients, states = NULL, transitions = NULL)

Arguments

Value

Returns an object of class hesim_data, which is a list of data tables for health economic simulation modeling.

Note

Each table must either be a data.frame or data.table. All ID variables within each table must be numeric vectors of integers and should be of the form 1,2,...N where N is the number of unique values of the ID variable.

See Also

expand.hesim_data(), get_labels()

Examples

strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3), age = c(65, 50, 75),
                       gender = c("Female", "Female", "Male"))
states <- data.frame(state_id =  seq(1, 3),
                     state_var = c(2, 1, 9))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)

List of survival distributions

Description

List of additional distributions for parametric survival analysis that are not contained in flexsurv. Can be used to fit models with flexsurv::flexsurvreg(). Same format as flexsurv::flexsurv.dists.

Usage

hesim_survdists

Format

A list with the following elements:

name

Name of the probability distribution.

pars

Vector of strings naming the parameters of the distribution. These must be the same names as the arguments of the density and probability functions.

location

Name of the location parameter.

transforms

List of R functions which transform the range of values taken by each parameter onto the real line. For example, c(log, log) for a distribution with two positive parameters.

inv.transforms

List of R functions defining the corresponding inverse transformations. Note these must be lists, even for single parameter distributions they should be supplied as, e.g. c(exp) or list(exp).

inits

A function of the observed survival times t (including right-censoring times, and using the halfway point for interval-censored times) which returns a vector of reasonable initial values for maximum likelihood estimation of each parameter. For example, function(t){ c(1, mean(t)) } will always initialize the first of two parameters at 1, and the second (a scale parameter, for instance) at the mean of t.

Individualized cost-effectiveness analysis

Description

These functions are deprecated, use cea() and cea_pw() instead.

Usage

icea(x, ...)

icea_pw(x, ...)

Arguments

Incremental cost-effectiveness ratio

Description

Generate a tidy table of incremental cost-effectiveness ratios (ICERs) given output from cea_pw() with icer() and format for pretty printing with format.icer().

Usage

icer(x, prob = 0.95, k = 50000, labels = NULL, ...)

## S3 method for class 'icer'
format(
  x,
  digits_qalys = 2,
  digits_costs = 0,
  pivot_from = "strategy",
  drop_grp = TRUE,
  pretty_names = TRUE,
  ...
)

Arguments

Details

Note that icer() will report negative ICERs; however, format() will correctly note whether a treatment strategy is dominated by or dominates the reference treatment.

Value

icer() returns an object of class icer that is a tidy data.table with the following columns:

strategy

The treatment strategy.

grp

The subgroup.

outcome

The outcome metric.

estimate

The point estimate computed as the average across the PSA samples.

lower

The lower limit of the confidence interval.

upper

The upper limit of the confidence interval.

format.icer() formats the table according to the arguments passed.

See Also

cea_pw()

ICER table

Description

Generate a table of incremental cost-effectiveness ratios given output from cea_pw().

Usage

icer_tbl(
  x,
  k = 50000,
  cri = TRUE,
  prob = 0.95,
  digits_qalys = 2,
  digits_costs = 0,
  output = c("matrix", "data.table"),
  rownames = NULL,
  colnames = NULL,
  drop = TRUE
)

Arguments

Value

If output = "matrix", then a list of matrices (or a matrix if drop = TRUE) reporting incremental cost-effectiveness ratios (ICERs) by group. Specifically, each matrix contains five rows for: (i) incremental quality-adjusted life-years (QALYs), (ii) incremental costs, (iii) the incremental net monetary benefit (NMB), (iv) the ICER, and (v) a conclusion stating whether each strategy is cost-effective relative to a comparator. The number of columns is equal to the number of strategies (including the comparator).

If output = "data.table", then the results are reported as a data.table, with one row for each strategy and group combination.

See Also

cea_pw()

Attributes for ID variables

Description

Stores metadata related to the ID variables used to index input_mats and transformed parameter objects already predicted from covariates.

Usage

id_attributes(
  strategy_id,
  n_strategies,
  patient_id,
  n_patients,
  state_id = NULL,
  n_states = NULL,
  transition_id = NULL,
  n_transitions = NULL,
  time_id = NULL,
  time_intervals = NULL,
  n_times = NULL,
  sample = NULL,
  n_samples = NULL,
  grp_id = NULL,
  patient_wt = NULL
)

Arguments

Details

When using the ID variables to index input_mats, the sorting order should be the same as specified in expand.hesim_data(); that is, observations must be sorted by prioritizing: (i) strategy_id, (ii) patient_id, (iii) the health-related ID variable (either state_id or transition_id), and (iv) time_id. When using ID variables are used to index transformed parameter objects and sample is used for indexing, then observations must be sorted by prioritizing: (i) sample, (ii) strategy_id, (iii) patient_id, (iv) the health-related ID variable, and (v) time_id.

See Also

hesim_data(),expand.hesim_data(), input_mats

Incremental treatment effect

Description

Computes incremental effect for all treatment strategies on outcome variables from a probabilistic sensitivity analysis relative to a comparator.

Usage

incr_effect(x, comparator, sample, strategy, grp = NULL, outcomes)

Arguments

Value

A data.table containing the differences in the values of each variable specified in outcomes between each treatment strategy and the comparator.

Examples

# simulation output
n_samples <- 100
sim <- data.frame(sample = rep(seq(n_samples), 4),
             c = c(rlnorm(n_samples, 5, .1), rlnorm(n_samples, 5, .1),
                    rlnorm(n_samples, 11, .1), rlnorm(n_samples, 11, .1)),
             e = c(rnorm(n_samples, 8, .2), rnorm(n_samples, 8.5, .1),
                   rnorm(n_samples, 11, .6), rnorm(n_samples, 11.5, .6)),
             strategy = rep(paste0("Strategy ", seq(1, 2)),
                           each = n_samples * 2),
             grp = rep(rep(c("Group 1", "Group 2"),
                           each = n_samples), 2)
)
# calculate incremental effect of Strategy 2 relative to Strategy 1 by group
ie <- incr_effect(sim, comparator = "Strategy 1", sample = "sample",
                        strategy = "strategy", grp = "grp", outcomes = c("c", "e"))
head(ie)

Code to use the hesim package inline. Not directly called by the user.

Description

Code to use the hesim package inline. Not directly called by the user.

Usage

inlineCxxPlugin(...)

Arguments

Examples

 ## Not run: 
  library(Rcpp)
  sourceCpp(code="
  // [[Rcpp::depends(hesim)]]
  // [[Rcpp::depends(RcppArmadillo)]]
  #include <hesim.h>
  // [[Rcpp::export]]
  double test_inline_gengamma(double mu, double sigma, double Q) {
    hesim::stats::gengamma gg(mu, sigma, Q);
    return gg.random();
  }")
  set.seed(12345)
  test_inline_gengamma(1.0, 1.0, 1.0)
  
## End(Not run)
  

Input matrices for a statistical model

Description

An object of class input_mats contains input matrices for simulating a statistical model. Consists of (i) input matrices, X, and (ii) metadata used to index each matrix in X.

Once created, an input_mats object can be converted to a data.table::data.table with as.data.table(), which is a helpful way to check that the object is as expected. The print() method summarizes the object and prints it to the console.

More details are provided under "Details" below.

Usage

input_mats(X, ...)

## S3 method for class 'input_mats'
as.data.table(x, ...)

## S3 method for class 'input_mats'
print(x, ...)

Arguments

Details

input_mats objects are used with params objects to simulate disease models, cost models, and/or utility models. Each column of ⁠$X⁠ contains variables from the params object and a given row corresponds to a combination of the ID variables. An input matrix must always have rows for the treatment strategies (strategy_id) and patients (patient_id); it may optionally have rows for health variables (state_id or transition_id) and time intervals (time_id). The rows must be sorted by prioritizing (i) strategy_id, (ii) patient_id, (iii) the health related ID variable (either state_id or transition_id) and (iv) time_id.

While input_mats objects can be created directly with input_mats(), it is rarely a good idea to do so. They are typically created as the input_data field when creating model objects (e.g., with create_IndivCtstmTrans(), create_CohortDtstmTrans(), and create_PsmCurves()). Internally, these functions create the input matrices using create_input_mats() methods, which ensure that they are in the correct format. Users may also use create_input_mats() methods, but there is not usually a good reason to do so.

as.data.table.input_mats() will convert input matrices into a single data.table() that column binds the ID variables and the unique combinations of variables contained in the elements of ⁠$X⁠. print.input_mats() prints a call to as.data.table() and provides additional information about the ID variables.

See Also

See IndivCtstmTrans() and PsmCurves() for examples in which the input_data field of an instance of a model class is an input_mats object.

Examples

library("data.table")

# Input matrices are typically created as part of model objects
# Let's illustrate with a partitioned survival model (PSM)

## Model setup
strategies <- data.frame(strategy_id = c(1, 2),
                         new_strategy = c(0, 1))
patients <- data.frame(patient_id = seq(1, 3),
                       age = c(45, 47, 60),
                       female = c(1, 0, 0),
                       group = factor(c("Good", "Medium", "Poor")))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients)

## Create survival models for PSM
### Parameters
n <- 2
survmod_params <- params_surv_list(
  # Progression free survival (PFS) 
  pfs = params_surv(
    coefs = list(
      rate = data.frame(intercept = rnorm(n, log(1/5), 1),
                        new_strategy = rnorm(n, log(.8), 1))
      ),
    dist = "exp"
  ),
  
  # Overall survival (OS)
  os = params_surv(
    coefs = list(
      rate = data.frame(intercept = rnorm(n, log(1/10), 1))
    ),
    dist = "exp"
  )
)

### Input data
survmod_input_data <- expand(hesim_dat)[, intercept := 1]

### Model object
survmod <- create_PsmCurves(survmod_params, input_data = survmod_input_data)

## Inspect input data
survmod$input_data # Print "input_mats" object to console
as.data.table(survmod$input_data) # Convert "input_mats" object to data.table

List of lm objects

Description

Combine lm objects into a list

Usage

lm_list(...)

Arguments

Value

Returns an object of class lm_list.

Examples

 dat <- psm4_exdata$costs$medical
 lm_fits <- lm_list(fit1 = stats::lm(costs ~ 1, data = dat), 
                    fit2 = stats::lm(costs ~ female, data = dat))
 class(lm_fits)

Method of moments for beta distribution

Description

Compute the parameters shape1 and shape2 of the beta distribution using method of moments given the mean and standard deviation of the random variable of interest.

Usage

mom_beta(mean, sd)

Arguments

Details

If \mu is the mean and \sigma is the standard deviation of the random variable, then the method of moments estimates of the parameters shape1 = \alpha > 0 and shape2 = \beta > 0 are:

\alpha = \mu \left(\frac{\mu(1-\mu)}{\sigma^2}-1 \right)

and

\beta = (1 - \mu) \left(\frac{\mu(1-\mu)}{\sigma^2}-1 \right)

Value

A list containing the parameters shape1 and shape2.

Examples

mom_beta(mean = .8, sd = .1)
# The function is vectorized.
mom_beta(mean = c(.6, .8), sd = c(.08, .1))

Method of moments for gamma distribution

Description

Compute the shape and scale (or rate) parameters of the gamma distribution using method of moments for the random variable of interest.

Usage

mom_gamma(mean, sd, scale = TRUE)

Arguments

Details

If \mu is the mean and \sigma is the standard deviation of the random variable, then the method of moments estimates of the parameters shape = \alpha > 0 and scale = \theta > 0 are:

\theta = \frac{\sigma^2}{\mu}

and

\alpha = \frac{\mu}{\theta}

The inverse of the scale parameter, \beta = 1/\theta, is the rate parameter.

Value

If scale = TRUE, then a list containing the parameters shape and scale; otherwise, if scale = FALSE, then a list containing the parameters shape and rate.

Examples

mom_gamma(mean = 10000, sd = 2000)
# The function is vectorized.
mom_gamma(mean = c(8000, 10000), sd = c(1500, 2000))

Example data for a reversible 3-state multi-state model

Description

Example multi-state data for parameterizing a continuous time state transition model. Costs and utility are also included to facilitate cost-effectiveness analysis.

Usage

mstate3_exdata

Format

A list containing the following elements:

transitions

A data frame containing the times at which patient transitions between health states based on the prothr dataset from the mstate package.

costs

A list of data frames. The first data frame contains summary medical cost estimates and the second data frame contains drug cost data.

utility

A data frame of summary utility estimates.

Transitions data

The data frame has the following columns:

strategy_id

Treatment strategy identification number.

patient_id

Patient identification number.

age

Patient age (in years).

female

1 if a patient is female; 0 if male.

from

Starting state.

to

Receiving state.

trans

Transition number.

Tstart

Starting time.

Tstop

Transition time.

years

Elapsed years between Tstart and Tstop.

status

Status variable; 1=transition, 0=censored.

Cost data

The cost list contains two data frames. The first data frame contains data on the drug costs associated with each treatment strategy.

strategy_id

The treatment strategy identification number.

costs

Annualized drug costs.

The second data frame contains summary data on medical costs by health state, and contains the following columns:

state_id

The health state identification number.

mean

Mean costs.

se

Standard error of medical costs.

Utility data

The data frame has the following columns:

state_id

The health state identification number.

mean

Mean utility

se

Standard error of utility

Example data for a 3-state multinomial model

Description

Example discrete time health state transitions data simulated using multinomial logistic regression. Costs and utility are also included to facilitate cost-effectiveness analysis.

Usage

multinom3_exdata

Format

A list containing the following elements:

transitions

A data frame containing patient transitions between health states at discrete time intervals (i.e., on a yearly basis).

costs

A list of data frames. The first data frame contains drug cost data and the second contains summary medical cost estimates.

utility

A data frame of summary utility estimates.

Transitions data

The data frame has the following columns:

patient_id

Patient identification number.

strategy_id

Treatment strategy identification number.

strategy_name

Treatment strategy name.

age

Patient age (in years).

age_cat

A factor variable with 3 age groups: (i) age less than 40, (ii) age at least 40 and less than 60, and (iii) age at least 60.

female

1 if a patient is female; 0 if male.

year

The year since the start of data collection with the first year equal to 1.

state_from

State making a transition from.

state_to

State making a transition to.

year_cat

Factor variable for year with 3 categories: (i) year 3 and below, (ii) year between 3 and 6, and (iii) year 7 and above.

Cost data

The cost list contains two data frames. The first data frame contains data on the drug costs associated with each treatment strategy.

strategy_id

The treatment strategy identification number.

strategy_name

The treatment strategy name.

costs

Annualized drug costs.

The second data frame contains summary data on medical costs by health state, and contains the following columns:

state_id

The health state identification number.

state_name

The name of the health state.

mean

Mean medical costs.

se

Standard error of medical costs.

Utility data

The data frame has the following columns:

state_id

The health state identification number.

state_name

The name of the health state.

mean

Mean utility

se

Standard error of utility.

List of multinom objects

Description

Combine multinom objects into a list.

Usage

multinom_list(...)

Arguments

Value

An object of class multinom_list.

Examples

 library("nnet")
 library("data.table")
 trans_data <- data.table(multinom3_exdata$transitions)
 dat_healthy <- trans_data[state_from == "Healthy"]
 fit_healthy <- multinom(state_to ~ strategy_name + female + age_cat + year_cat, 
                          data = dat_healthy)
 dat_sick <- trans_data[state_from == "Sick"]
 dat_sick$state_to <- droplevels(dat_sick$state_to)
 fit_sick <- multinom(state_to ~ strategy_name + female + age_cat + year_cat, 
                      data = dat_sick)
 fits <- multinom_list(healthy = fit_healthy, sick = fit_sick)
 class(fits)

Draw parameters of statistical model from multivariate normal distribution

Description

normboot is a generic function for drawing parameters from a fitted statistical model from their (asymptotic) multivariate normal distribution.

Usage

normboot(object, B, ...)

## S3 method for class 'msm'
normboot(object, B = 1000, ...)

Arguments

Multi-state oncology data for 3-state model

Description

Simulated 3-state dataset in oncology with three health states (Stable, Progression, and Death) and three possible transitions (Stable -> Progression, Stable -> Death, and Progression -> Death).

Usage

onc3

Format

A data.table with the following columns:

from

Health state making a transition from.

to

Health state making a transition to.

strategy_name

Standard of care (SOC), new treatment 1 (New 1), or new treatment 2 (New 2).

female

1 if a patient is female; 0 if male.

age

Patient age (in years).

patient_id

Patient identification number.

time_start

Starting time.

time_stop

Stopping time.

status

Status indicator: 1=transition, 0=censored.

transition_id

Integer denoting transition: 1 = Stable -> Progression, 2 = Stable -> Death, 3 = Progression -> Death.

strategy_id

Strategy identification number.

time

Elapsed years between time_start and time_stop.

See Also

onc3p

Examples

head(onc3)

Multi-state panel oncology data for 3-state model

Description

The same dataset as onc3 converted into a panel data format in which health states are recorded at a finite series of times.

Usage

onc3p

Format

A data.table with the following columns:

state

The name of the health state (Stable, Progression, and Death).

strategy_name

Standard of care (SOC), new treatment 1 (New 1), or new treatment 2 (New 2).

female

1 if a patient is female; 0 if male.

age

Patient age (in years).

patient_id

Patient identification number.

time

Time that state was recorded.

strategy_id

Strategy identification number.

state_id

The health state identification number.

See Also

onc3

Examples

head(onc3p)

Parameter object

Description

Objects prefixed by "params_" are lists containing the parameters of a statistical model used for simulation modeling. The parameters are used to simulate outcomes as a function of covariates contained in input matrices (input_mats).

See Also

tparams

Parameters of a linear model

Description

Create a list containing the parameters of a fitted linear regression model.

Usage

params_lm(coefs, sigma = 1)

Arguments

Details

Fitted linear models are used to predict values, y, as a function of covariates, x,

y = x^T\beta + \epsilon.

Predicted means are given by x^T\hat{\beta} where \hat{\beta} is the vector of estimated regression coefficients. Random samples are obtained by sampling the error term from a normal distribution, \epsilon \sim N(0, \hat{\sigma}^2).

Value

An object of class params_lm, which is a list containing coefs, sigma, and n_samples. n_samples is equal to the number of rows in coefs. The coefs element is always converted into a matrix.

See Also

This parameter object is useful for modeling health state values when values can vary across patients and/or health states as a function of covariates. In many cases it will, however, be simpler, and more flexible to use a stateval_tbl. For an example use case see the documentation for create_StateVals.lm().

Examples

library("MASS")
n <- 2
params <- params_lm(
  coefs = mvrnorm(n, mu = c(.5,.6),
                  Sigma = matrix(c(.05, .01, .01, .05), nrow = 2)),
  sigma <- rgamma(n, shape = .5, rate = 4)
)
summary(params)
params

Parameters of a multinomial logit model

Description

Store the parameters of a fitted multinomial logistic regression model. The model is used to predict probabilities of K classes, which represent the probability of transitioning to particular health state in a discrete time state transition model. Can be used as an element of a params_mlogit_list to parameterize a CohortDtstmTrans object.

Usage

params_mlogit(coefs)

Arguments

Details

Multinomial logit models are used to predict the probability of membership for subject i in each of K classes as a function of covariates:

Pr(y_i = c) = \frac{e^{\beta_c x_i}}{\sum_{k=1}^K e^{\beta_k x_i}}

Value

An object of class params_mlogit, which is a list containing coefs and n_samples, where n_samples is equal to the number of rows in each element of coefs. The coefs element is always converted into a 3D array of stacked matrices.

See Also

summary.params_mlogit(), params_mlogit_list(), CohortDtstmTrans

Examples

# Consider a sick-sicker model and model transitions from the sick state

## We can instantiate from a list of data frames
params <- params_mlogit(
  coefs = list(
    ### Transition from sick to sicker
    sicker = data.frame(
      intercept = c(-0.33, -.2, -.15),
      treat = c(log(.75), log(.8), log(.9))
    ),
    
   ### Transition from sick to death
    death = data.frame(
      intercept = c(-1, -1.2, -.5),
      treat = c(log(.6), log(.65), log(.55))
    )
  )
)
summary(params)
params

## We can also instantiate from an array
coefs_sicker <- data.frame(
  intercept = c(-0.33, -.2, -.15),
  treat = c(log(.75), log(.8), log(.9))
)
coefs_death <- data.frame(
  intercept = c(-1, -1.2, -.5),
  treat = c(log(.6), log(.65), log(.55))
)

params2 <- params_mlogit(
  coefs <- array(
    data = c(as.matrix(coefs_sicker),
             as.matrix(coefs_death)),
    dim = c(3, 2, 2),
    dimnames = list(NULL, c("intercept", "treat"), c("sicker", "death"))
  )
)
params2

Parameters of a list of multinomial logit models

Description

Create a list containing the parameters of multiple fitted multinomial logit models. Can be used to parameterize state transitions in a discrete time transition model by passing to the params field of a CohortDtstmTrans object.

Usage

params_mlogit_list(...)

Arguments

Value

An object of class params_mlogit_list, which is a list containing params_mlogit objects.

See Also

summary.params_mlogit_list(), params_mlogit(), CohortDtstmTrans

Examples

# Consider a sick-sicker model

params <- params_mlogit_list(
  ## Transitions from sick state (sick -> sicker, sick -> death)
  sick = params_mlogit(
    coefs = list(
      sicker = data.frame(
        intercept = c(-0.33, -.2),
        treat = c(log(.75), log(.8))
      ),
      death = data.frame(
        intercept = c(-1, -1.2),
        treat = c(log(.6), log(.65))
      )
    )
  ),
  
  ## Transitions from sicker state (sicker -> death)
  sicker = params_mlogit(
    coefs = list(
      death = data.frame(
        intercept = c(-1.5, -1.4),
        treat = c(log(.5), log(.55))
      )
    )
  )
)
summary(params)
params

Parameters of a survival model

Description

Create a list containing the parameters of a single fitted parametric or flexible parametric survival model.

Usage

params_surv(coefs, dist, aux = NULL)

Arguments

Details

Survival is modeled as a function of L parameters \alpha_l. Letting F(t) be the cumulative distribution function, survival at time t is given by

1 - F(t | \alpha_1(x_{1}), \ldots, \alpha_L(x_{L})).

The parameters are modeled as a function of covariates, x_l, with an inverse transformation function g^{-1}(),

\alpha_l = g^{-1}(x_{l}^T \beta_l).

g^{-1}() is typically exp() if a parameter is strictly positive and the identity function if the parameter space is unrestricted.

The types of distributions that can be specified are:

exponential or exp

Exponential distribution. coef must contain the rate parameter on the log scale and the same parameterization as in stats::Exponential.

weibull or weibull.quiet

Weibull distribution. The first element of coef is the shape parameter (on the log scale) and the second element is the scale parameter (also on the log scale). The parameterization is that same as in stats::Weibull.

weibullPH

Weibull distribution with a proportional hazards parameterization. The first element of coef is the shape parameter (on the log scale) and the second element is the scale parameter (also on the log scale). The parameterization is that same as in flexsurv::WeibullPH.

gamma

Gamma distribution. The first element of coef is the shape parameter (on the log scale) and the second element is the rate parameter (also on the log scale). The parameterization is that same as in stats::GammaDist.

lnorm

Lognormal distribution. The first element of coef is the meanlog parameter (i.e., the mean of survival on the log scale) and the second element is the sdlog parameter (i.e., the standard deviation of survival on the log scale). The parameterization is that same as in stats::Lognormal. The coefficients predicting the meanlog parameter are untransformed whereas the coefficients predicting the sdlog parameter are defined on the log scale.

gompertz

Gompertz distribution. The first element of coef is the shape parameter and the second element is the rate parameter (on the log scale). The parameterization is that same as in flexsurv::Gompertz.

llogis

Log-logistic distribution. The first element of coef is the shape parameter (on the log scale) and the second element is the scale parameter (also on the log scale). The parameterization is that same as in flexsurv::Llogis.

gengamma

Generalized gamma distribution. The first element of coef is the location parameter mu, the second element is the scale parameter sigma (on the log scale), and the third element is the shape parameter Q. The parameterization is that same as in flexsurv::GenGamma.

survspline

Survival splines. Each element of coef is a parameter of the spline model (i.e. gamma_0, gamma_1, \ldots) with length equal to the number of knots (including the boundary knots). See below for details on the auxiliary arguments. The parameterization is that same as in flexsurv::Survspline.

fracpoly

Fractional polynomials. Each element of coef is a parameter of the fractional polynomial model (i.e. gamma_0, gamma_1, \ldots) with length equal to the number of powers plus 1. See below for details on the auxiliary arguments (i.e., powers).

pwexp

Piecewise exponential distribution. Each element of coef is rate parameter for a distinct time interval. The times at which the rates change should be specified with the auxiliary argument time (see below for more details)

.

fixed

A fixed survival time. Can be used for "non-random" number generation. coef should contain a single parameter, est, of the fixed survival times.

Auxiliary arguments for spline models should be specified as a list containing the elements:

knots

A numeric vector of knots.

scale

The survival outcome to be modeled as a spline function. Options are "log_cumhazard" for the log cumulative hazard; "log_hazard" for the log hazard rate; "log_cumodds" for the log cumulative odds; and "inv_normal" for the inverse normal distribution function.

timescale

If "log" (the default), then survival is modeled as a spline function of log time; if "identity", then it is modeled as a spline function of time.

Auxiliary arguments for fractional polynomial models should be specified as a list containing the elements:

powers

A vector of the powers of the fractional polynomial with each element chosen from the following set: -2. -1, -0.5, 0, 0.5, 1, 2, 3.

Auxiliary arguments for piecewise exponential models should be specified as a list containing the element:

time

A vector equal to the number of rate parameters giving the times at which the rate changes.

Furthermore, when splines (with scale = "log_hazard") or fractional polynomials are used, numerical methods must be used to compute the cumulative hazard and for random number generation. The following additional auxiliary arguments can therefore be specified:

cumhaz_method

Numerical method used to compute cumulative hazard (i.e., to integrate the hazard function). Always used for fractional polynomials but only used for splines if scale = "log_hazard". Options are "quad" for adaptive quadrature and "riemann" for Riemann sum.

random_method

Method used to randomly draw from an arbitrary survival function. Options are "invcdf" for the inverse CDF and "discrete" for a discrete time approximation that randomly samples events from a Bernoulli distribution at discrete times.

step

Step size for computation of cumulative hazard with numerical integration. Only required when using "riemann" to compute the cumulative hazard or using "discrete" for random number generation.

Value

An object of class params_surv, which is a list containing coefs, dist, and n_samples. n_samples is equal to the number of rows in each element of coefs, which must be the same. The coefs element is always converted into a list of matrices. The list may also contain aux if a spline, fractional polynomial, or piecewise exponential model is used.

Examples

n <- 10
params <- params_surv(
  coefs = list(
    shape = data.frame(
      intercept = rnorm(n, .5, .23)
    ),
    scale = data.frame(
      intercept = rnorm(n, 12.39, 1.49),
      age = rnorm(n, -.09, .023)
   )
  ),
  dist = "weibull"
)
summary(params)
params

Parameters of a list of survival models

Description

Create a list containing the parameters of multiple fitted parametric survival models.

Usage

params_surv_list(...)

Arguments

Value

An object of class params_surv_list, which is a list containing params_surv objects.

See Also

create_params()

Examples

n <- 5
params <- params_surv_list(
  # Model for progression free survival
  pfs = params_surv(
    coefs = list(
      rate = data.frame(intercept = rnorm(n, log(.5), .5),
                        new_strategy = rnorm(n, log(.8), .1))
   ),
    dist = "exp"
  ),
 
  # Model for overall survival
  os = params_surv(
    coefs = list(
      rate = data.frame(intercept = rnorm(n, log(.3) , .5))
    ),
    dist = "exp"
  )
)
summary(params)
params

Partitioned survival regression object

Description

Create a partitioned survival regression object of class partsurvfit. The object contains a list of fitted survival models fit using either flexsurvreg or flexsurvspline (i.e., an object of class flexsurvreg_list) and the data frame used to perform the fit of each model. The same data frame must have been used for each fit.

Usage

partsurvfit(object, data)

Arguments

Value

Returns an object of class partsurvfit, which is a list containing two elements. The first element, "models", contains the survival models passed to object, and the second element, "data" contains the data frame passed to data.

Examples

library("flexsurv")
fit1 <- flexsurv::flexsurvreg(formula = Surv(endpoint1_time, endpoint1_status) ~ age, 
                              data = psm4_exdata$survival,
                              dist = "weibull")
fit2 <- flexsurv::flexsurvreg(formula = Surv(endpoint2_time, endpoint2_status) ~ age, 
                              data = psm4_exdata$survival, 
                              dist = "weibull")
fsreg_list <- flexsurvreg_list(endpoint1 = fit1, endpoint2 = fit2)
fits <- partsurvfit(fsreg_list, data = psm4_exdata$survival)
class(fits)

Plot cost-effectiveness acceptability curve

Description

Plot a cost-effectiveness curve from either the output of cea() or cea_pw() using ggplot2::ggplot. The former compares all treatment strategies simultaneously and uses the probabilistic sensitivity analysis (PSA) to compute the probability that each strategy is the most cost-effective at a given willingness to pay value, while the latter uses the PSA to compute the probability that each treatment is cost-effective relative to a comparator.

Usage

plot_ceac(x, ...)

## S3 method for class 'cea_pw'
plot_ceac(x, labels = NULL, ...)

## S3 method for class 'cea'
plot_ceac(x, labels = NULL, ...)

Arguments

Details

See the cea() documentation for an example. If there are multiple subgroups, then a faceted plot is produced with one plot for each subgroup.

Plot cost-effectiveness acceptability frontier

Description

Plot a cost-effectiveness acceptability frontier (CEAF) from the output of cea using ggplot2::ggplot. The CEAF plots the probability that the optimal treatment strategy (i.e., the strategy with the highest expected net monetary benefit) is cost-effective.

Usage

plot_ceaf(x, labels = NULL)

Arguments

Details

See the cea() documentation for an example. If there are multiple subgroups, then a faceted plot is produced with one plot for each subgroup.

Value

A ggplot object.

Plot cost-effectiveness plane

Description

Plot a cost-effectiveness plane from the output of cea_pw() using ggplot2::ggplot. Each point is a random draw of incremental costs (y-axis) and incremental QALYs (x-axis) from a probabilistic sensitivity analysis.

Usage

plot_ceplane(x, k = 50000, labels = NULL)

Arguments

Details

See the cea_pw() documentation for an example. If there are multiple subgroups, then a faceted plot is produced with one plot for each subgroup.

Value

A ggplot object.

Plot expected value of perfect information

Description

Plot the expected value of perfect information (EVPI) from the output of cea() using ggplot2::ggplot. Intuitively, the EVPI provides an estimate of the amount that a decision maker would be willing to pay to collect additional data and completely eliminate uncertainty.

Usage

plot_evpi(x, labels = NULL)

Arguments

Details

See the cea() documentation for an example. If there are multiple subgroups, then a faceted plot is produced with one plot for each subgroup.

Value

A ggplot object.

Example data for a 4-state partitioned survival model

Description

A collection of example datasets containing simulated survival, costs, and utility data for a 4-state partitioned survival model.

Usage

psm4_exdata

Format

A list containing the following elements:

Survival

A data frame containing patient information and time to 3 separate survival endpoints.

Costs

A list of data frames. The first data frame contains medical cost data and the second data frame contains drug cost data.

Survival data

The survival data frame contains a list of 3 survival curves, each containing the following columns.

female

An indicator variable equal to 1 if the patient is female and 0 otherwise.

age

The age of the patient in years.

strategy_id

The id of the treatment strategy used.

endpoint1_time

Follow up time with right censored data to survival endpoint 1.

endpoint1_status

A status indicator for survival endpoint 1 equal to 0 if alive and 1 if dead.

endpoint2_time

Follow up time with right censored data to survival endpoint 2.

endpoint2_status

A status indicator for survival endpoint 2 equal to 0 if alive and 1 if dead.

endpoint3_time

Follow up time with right censored data to survival endpoint 3.

endpoint3_status

A status indicator for survival endpoint 3 equal to 0 if alive and 1 if dead.

Cost data

The cost list contains two data frames.The first data frame contains data on the medical costs by patient and health state, and contains the following columns:

patient_id

An integer denoting the id of the patient.

female

An indicator variable equal to 1 if the patient is female and 0 otherwise.

state_name

A categorical variable denoting the three possible health states.

costs

Annualized medical costs.

The second data frame contains data on the drug costs associated with each treatment strategy.

strategy_id

The id of each treatment strategy.

costs

Annualized drug costs.

Quality-adjusted life-years object

Description

An object of class qalys returned from methods ⁠$sim_qalys()⁠ in model classes that store simulated quality-adjusted life-years (QALYs).

Components

A qalys object inherits from data.table and contains the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

grp_id

The subgroup ID.

state_id

The health state ID.

dr

The rate used to discount QALYs.

category

A single category always equal to "qalys".

qalys

The simulated values of QALYs.

If the argument lys = TRUE, then the data.table also contains a column lys containing simulated life-years.

Transition intensity matrix

Description

A generic function for creating transition intensity matrices where elements represent the instantaneous risk of moving between health states.

Usage

qmatrix(x, ...)

Arguments

Transition intensity matrix from tabular object

Description

Creates transition intensity matrices where elements represent the instantaneous risk of moving between health states.

Usage

## S3 method for class 'matrix'
qmatrix(x, trans_mat, ...)

## S3 method for class 'data.table'
qmatrix(x, trans_mat, ...)

## S3 method for class 'data.frame'
qmatrix(x, trans_mat, ...)

Arguments

Details

The object x must only contain non-zero and non-diagonal elements of a transition intensity matrix. The diagonal elements are automatically computed as the negative sum of the other rows.

Value

An array of transition intensity matrices with the third dimension equal to the number of rows in x.

See Also

qmatrix.msm()

Examples

# 3 state irreversible model
tmat <- rbind(c(NA, 1, 2),
              c(NA, NA, 3),
              c(NA, NA, NA)) 
q12 <- c(.8, .7)
q13 <- c(.2, .3)
q23 <- c(1.1, 1.2)
q <- data.frame(q12, q13, q23)
qmat <- qmatrix(q, trans_mat = tmat)
print(qmat)

# Matrix exponential of each matrix in array
expmat(qmat)

Transition intensity matrix from msm object

Description

Draw transition intensity matrices for a probabilistic sensitivity analysis from a fitted msm object.

Usage

## S3 method for class 'msm'
qmatrix(x, newdata = NULL, uncertainty = c("normal", "none"), n = 1000, ...)

Arguments

Value

An array of transition intensity matrices with the third dimension equal to the number of rows in newdata.

See Also

qmatrix.matrix()

Examples

library("msm")
set.seed(101)
 qinit <- rbind(
   c(0, 0.28163, 0.01239),
   c(0, 0, 0.10204),
   c(0, 0, 0)
 )
fit <- msm(state_id ~ time, subject = patient_id, 
           data = onc3p[patient_id %in% sample(patient_id, 100)],
           covariates = list("1-2" =~ age + strategy_name), 
           qmatrix = qinit)
qmatrix(fit, newdata = data.frame(age = 55, strategy_name = "New 1"),
        uncertainty = "none")
qmatrix(fit, newdata = data.frame(age = 55, strategy_name = "New 1"),
        uncertainty = "normal",  n = 3)

Random generation for categorical distribution

Description

Draw random samples from a categorical distribution given a matrix of probabilities. rcat is vectorized and written in C++ for speed.

Usage

rcat(n, prob)

Arguments

Value

A vector of random samples from the categorical distribution. The length of the sample is determined by n. The numerical arguments other than n are recycled so that the number of samples is equal to n.

Examples

p <- c(.2, .5, .3)
n <- 10000
pmat <- matrix(rep(p, n), nrow = n, ncol = length(p), byrow = TRUE)

# rcat
set.seed(100)
ptm <- proc.time()
samp1 <- rcat(n, pmat)
proc.time() - ptm
prop.table(table(samp1))

# rmultinom from base R 
set.seed(100)
ptm <- proc.time()
samp2 <- t(apply(pmat, 1, rmultinom, n = 1, size = 1))
samp2 <- apply(samp2, 1, function(x) which(x == 1))
proc.time() - ptm
prop.table(table(samp2))

Random generation for multiple Dirichlet distributions

Description

Draw random samples from multiple Dirichlet distributions for use in transition probability matrices.

Usage

rdirichlet_mat(
  n,
  alpha,
  output = c("array", "matrix", "data.frame", "data.table")
)

Arguments

Details

This function is meant for representing the distribution of transition probabilities in a transition matrix. The ⁠(i,j)⁠ element of alpha is a transition from state i to state j. It is vectorized and written in ⁠C++⁠ for speed.

Value

If output = "array", then an array of matrices is returned where each row of each matrix is a sample from the Dirichlet distribution. If output results in a two dimensional object (i.e., a matrix, data.frame, or data.table, then each row contains all elements of the sampled matrix from the Dirichlet distribution ordered rowwise; that is, each matrix is flattened. In these cases, the number of rows must be less than or equal to the number of columns.

Examples

alpha <- matrix(c(100, 200, 500, 50, 70, 75), ncol = 3, nrow = 2, byrow = TRUE)
samp <- rdirichlet_mat(100, alpha)
print(samp[, , 1:2])

Objects exported from other packages

Description

These objects are imported from other packages. Follow the links below to see their documentation.

data.table

as.data.table

ggplot2

autoplot

Random number generation distributions

Description

A collection of functions for randomly generating deviates from probability distributions with define_rng().

Usage

beta_rng(
  shape1 = 1,
  shape2 = 1,
  mean = NULL,
  sd = NULL,
  names = NULL,
  n = parent.frame()$n
)

dirichlet_rng(alpha, names = NULL, n = parent.frame()$n)

fixed(est, names = NULL, n = parent.frame()$n)

custom(x, names = NULL, n = parent.frame()$n)

gamma_rng(mean, sd, names = NULL, n = parent.frame()$n)

lognormal_rng(meanlog, sdlog, names = NULL, n = parent.frame()$n)

multi_normal_rng(mu, Sigma, names = NULL, n = parent.frame()$n, ...)

normal_rng(mean, sd, names = NULL, n = parent.frame()$n)

uniform_rng(min, max, names = NULL, n = parent.frame()$n)

Arguments

Details

These functions are not exported and are meant for use with define_rng(). They consequently assume that the number of samples to draw, n, is defined in the parent environment. Convenience random number generation functions include:

beta_rng()

If mean and sd are both not NULL, then parameters of the beta distribution are derived using the methods of moments with mom_beta(). Beta variates are generated with stats::rbeta().

custom()

Use previously sampled values from a custom probability distribution. There are three possibilities: (i) if n is equal to the number previously sampled values (say n_samples), then x is returned as is; (ii) if n < n_samples, then samples from x are sampled without replacement; and (iii) if n > n_samples, then samples from x are sampled with replacement and a warning is provided.

dirichlet_rng()

Dirichlet variates for each row in the matrix are generated with rdirichlet_mat(). The sampled values are stored in a data.table where there is a column for each element of alpha (with elements ordered rowwise).

fixed()

This function should be used when values of the variable of interest are fixed (i.e., they are known with certainty). If length(est) > 1, an n by length(est) data.table is returned meaning that each element of est is repeated n times; otherwise (if length(est) == 1), a vector is returned where est is repeated n times.

gamma_rng()

The parameters of the gamma distribution are derived using the methods of moments with mom_gamma() and gamma variates are generated with stats::rgamma().

lognormal_rng()

Lognormal variates are generated with stats::rlnorm().

multi_normal_rng()

Multivariate normal variates are generated with MASS::mvrnorm().

normal_rng()

Normal variates are generated with stats::rnorm().

uniform_rng()

Uniform variates are generated with stats::runif().

Value

Functions either return a vector of length n or an n by k data.table. Multivariate distributions always return a data.table. If a univariate distribution is used, then a data.table is returned if each parameter is specified as a vector with length greater than 1; otherwise, if parameters are scalars, then a vector is returned. In the data.table case, k is equal to the length of the parameter vectors entered as arguments. For example, if the probability distribution contained mean as an argument and mean were of length 3, then an n by 3 matrix would be returned. The length of all parameter vectors must be the same. For instance, if the vector mean were of length 3 then all additional parameters (e.g., sd) must also be of length 3.

If a data.table is returned by a distribution, then its column names are set according to the following hierarchy:

1. With the names argument if it is not NULL

2. With the names of the parameter vectors if they are named vectors. If there are multiple parameter vector arguments, then the names of the first parameter vector with non NULL names is used. For instance, if mean and sd are both arguments to a random number generation function and mean is a named vector, then the names from the vector mean are used.

3. As v1, ..., vk if the names argument is NULL and there are no named parameter vectors.

See Also

define_rng()

Random generation for piecewise exponential distribution

Description

Draw random samples from an exponential distribution with piecewise rates. rpwexp is vectorized and written in C++ for speed.

Usage

rpwexp(n, rate = 1, time = 0)

Arguments

Value

A vector of random samples from the piecewise exponential distribution. The length of the sample is determined by n. The numerical arguments other than n are recycled so that the number of samples is equal to n.

Examples

rate <- c(.6, 1.2, 1.3)
n <- 100000
ratemat <- matrix(rep(rate, n/2), nrow = n, 
                  ncol = 3, byrow = TRUE)
t <- c(0, 10, 15) 
ptm <- proc.time()
samp <- rpwexp(n, ratemat, t)
proc.time() - ptm
summary(samp)

Set value labels

Description

Update existing variables or create new ones that replace existing values with more informative labels as in factor(). All modifications are performed by reference (see data.table::set() for more information about assignment by reference).

Usage

set_labels(x, labels, new_names = NULL, as_factor = TRUE)

Arguments

Value

x is modified by reference and returned invisibly.

See Also

get_labels()

Examples

library("data.table")
labs <- list("strategy_id" = c("s1" = 1, 
                               "s2" = 2),
            "grp_id" = c("g1" = 1, 
                         "g2" = 2))
d1 <- data.table(strategy_id = 1:2, grp_id = 1:2)
d2 <- copy(d1); d3 <- copy(d2)
set_labels(d2, labels = labs)
set_labels(d3, labels = labs, new_names = c("strategy_name", "grp_name"))
d1
d2
d3

Expected values from state probabilities

Description

Simulate expected values as a function of simulated state occupancy probabilities, with simulation of costs and quality-adjusted life-years (QALYs) as particular use cases.

Usage

## S3 method for class 'stateprobs'
sim_ev(
  object,
  models = NULL,
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right"),
  value_name = "value",
  outcome_name = "outcome",
  ...
)

sim_qalys(
  object,
  model,
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right"),
  lys = TRUE
)

sim_costs(
  object,
  models,
  dr = 0.03,
  integrate_method = c("trapz", "riemann_left", "riemann_right")
)

Arguments

Details

Expected values in cohort models (i.e., those implemented with the CohortDtstm and Psm classes) are mean outcomes for patients comprising the cohort. The method used to simulate expected values depends on the ⁠$method⁠ field in the StateVals object(s) stored in model(s). If ⁠$method = "starting"⁠, then state values represent a one-time value that occurs at time 0.

The more common use case is ⁠$method = "wlos"⁠, or a "weighted length of stay". That is, expected values for each health state can be thought of as state values weighted by the time a patient spends in each state (and discounted by a discount factor that depends on the discount rate dr). The precise computation proceeds in four steps. In the first step, the probability of being in each health state at each discrete time point is simulated (this is the output contained in the stateprobs object). Second, a StateVals model is used to predict state values at each time point. Third an expected value at each time point is computed by multiplying the state probability, the state value, and the discount factor. Fourth, the expected values at each time point are summed across all time points.

The summation in the fourth step can be thought of as a discrete approximation of an integral. In particular, the limits of integration can be partitioned into time intervals, with each interval containing a start and an end. The integrate_method argument determines the approach used for this approximation:

1. A left Riemann sum (integrate_method = "riemann_left") uses expected values at the start of each time interval.

2. A right Riemann sum (integrate_method = "riemann_right") uses expected values at the end of each time interval.

3. The trapezoid rule (integrate_method = "trapz") averages expected values at the start and end of each time interval. (This will generally be the most accurate and is recommended.)

Mathematical details are provided in the reference within the "References" section below.

Value

sim_ev() returns a data.table with the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

grp_id

The subgroup ID.

state_id

The health state ID.

dr

The rate used to discount costs.

outcome

The outcome corresponding to each model in models. Only included if models is a list.

value

The expected value.

The names of the outcome and value columns may be changed with the value_name and outcome_name arguments. sim_costs() and sim_qalys() return similar objects, that are of class costs and qalys, respectively.

Note

The ID variables in the state value models in models must be consistent with the ID variables contained in object. In particular, the models should predict state values for each non-absorbing health state in object; that is, the number of health states modeled with the models should equal the number of health states in object less the number of absorbing states.

The absorbing states are saved as an attribute named absorbing to stateprobs objects. When simulating state probabilities with a CohortDtstmTrans object, the absorbing state is determined by the absorbing field in the class; in a Psm (or with sim_stateprobs.survival()), the absorbing state is always equal to the final health state.

References

Incerti and Jansen (2021). See Section 2.1 for mathematical details.

See Also

State probabilities can be simulated using the ⁠$sim_stateprobs()⁠ methods from either the CohortDtstmTrans (or CohortDtstm) or Psm classes. State probabilities can also be computed directly from survival curves with the generic method sim_stateprobs.survival().

Costs and QALYs are typically computed within the R6 model classes using the ⁠$sim_costs()⁠ and ⁠$sim_qalys()⁠ methods. For instance, see the documentation and examples for the CohortDtstm and Psm classes. The sim_qalys() and sim_costs() functions are exported to give users additional flexibility when creating their own modeling pipelines. sim_ev() may be useful for computing outcomes other than costs or QALYs.

costs and qalys objects can be passed to summarize_ce() to create a cost-effectiveness object for performing a cost-effectiveness analysis with cea(). Although note that typically the ⁠$summarize()⁠ method belonging to the CohortDtstm or Psm classes would be used instead.

Use the IndivCtstm class to simulate costs and QALYs with an individual continuous-time state transition model.

Examples

# We need (i) a state probability object and (ii) a model for state values
## We should start by setting up our decision problem
hesim_dat <-  hesim_data(strategies = data.frame(strategy_id = 1:2),
                         patients = data.frame(patient_id = 1:3),
                         states = data.frame(state_id = 1))
input_data <- expand(hesim_dat, by = c("strategies", "patients"))

## (i) Simulate a state probability object
tpmat_id <- tpmatrix_id(input_data, n_samples = 2) 
p_12 <- ifelse(tpmat_id$strategy_id == 1, .15, .1)
tpmat <- tpmatrix(
  C, p_12,
  0, 1
)
transmod <- CohortDtstmTrans$new(params = tparams_transprobs(tpmat, tpmat_id))
stprobs <- transmod$sim_stateprobs(n_cycles = 3)

## Construct model for state values
outcome_tbl <- stateval_tbl(
  data.frame(
    state_id = 1,
    est = 5000
  ),
  dist = "fixed"
)
outmod <- create_StateVals(outcome_tbl, n = 2, hesim_data = hesim_dat)

# We can then simulate expected values
## The generic expected values function
sim_ev(stprobs, models = outmod)

## We can also pass a list of models
sim_ev(stprobs, models = list(`Outcome 1` = outmod))

## Suppose the outcome were a cost category. Then we might
## prefer the following:
sim_costs(stprobs, models = list(drug = outmod))

## Length of stay is computed if there is no state value model
sim_ev(stprobs)

Simulated state probabilities

Description

A generic function to simulate state probabilities and create an object of class stateprobs.

Usage

sim_stateprobs(x, ...)

Arguments

Value

A stateprobs object.

See Also

sim_stateprobs.survival

Simulate state probabilities from survival curves

Description

Simulate health state probabilities from a survival object using partitioned survival analysis.

Usage

## S3 method for class 'survival'
sim_stateprobs(x, ...)

Arguments

Details

In an N-state partitioned survival model there are N-1 survival curves and S_n(t) is the cumulative survival function denoting the probability of survival to health state n or a lower indexed state beyond time t. The probability that a patient is in health state 1 at time t is simply S_1(t). State membership in health states 2,\ldots, N -1 is calculated as S_n(t) - S_{n-1}(t). Finally, the probability of being in the final health state N (i.e., the death state) is 1-S_{N-1}(t), or one minus the overall survival curve.

In some cases, the survival curves may cross. hesim will issue a warning but the function will still run. Probabilities will be set to 0 in a health state if the prior survival curve lies above the curve for state n; that is, if S_n(t) < S_{n-1}(t), then the probability of being in state n is set to 0 and S_n(t) is adjusted to equal S_{n-1}(t). The probability of being in the final health state is also adjusted if necessary to ensure that probabilities sum to 1.

Value

A stateprobs object.

See Also

survival

Examples

library("data.table")
library("survival")

# This example shows how to simulate a partitioned survival model by
# manually constructing a "survival" object. We will consider a case in which
# Cox proportional hazards models from the survival package---which are not
# integrated with hesim---are used for parameter estimation. We will use 
# point estimates in the example, but bootstrapping, Bayesian modeling,
# or other techniques could be used to draw samples for a probabilistic 
# sensitivity analysis. 

# (0) We first setup our model per usual by defining the treatment strategies,
# target population, and health states
hesim_dat <- hesim_data(
  strategies = data.table(strategy_id = 1:3,
                          strategy_name = c("SOC", "New 1", "New 2")),
  patients = data.table(patient_id = 1:2,
                        female = c(0, 1),
                        grp_id = 1),
  states = data.table(state_id = 1:2,
                      state_name = c("Stable", "Progression"))
)

# (1) Next we will estimate Cox models with survival::coxph(). We illustrate 
# by predicting progression free survival (PFS) and overall survival (OS)
## Fit models
onc3_pfs_os <- as_pfs_os(onc3, patient_vars = c("patient_id", "female",
                                                "strategy_name"))
fit_pfs <- coxph(Surv(pfs_time, pfs_status) ~ strategy_name + female,
                 data = onc3_pfs_os)
fit_os <- coxph(Surv(os_time, pfs_status) ~ strategy_name + female,
                data = onc3_pfs_os)

## Predict survival on input data
surv_input_data <- expand(hesim_dat)
times <- seq(0, 14, 1/12)
predict_survival <- function(object, newdata, times) {
  surv <- summary(survfit(object, newdata = newdata, se.fit = FALSE),
                  t = times)
  pred <- newdata[rep(seq_len(nrow(newdata)), each = length(times)), ]
  pred[, sample := 1] # Point estimates only in this example
  pred[, time := rep(surv$time, times = nrow(newdata))]
  pred[, survival := c(surv$surv)]
  return(pred[, ])
}
pfs <- predict_survival(fit_pfs, newdata = surv_input_data, times = times)
os <- predict_survival(fit_os, newdata = surv_input_data, times = times)
surv <- rbind(
  as.data.table(pfs)[, curve := 1L],
  as.data.table(os)[, curve := 2L]
)

## Convert predictions to a survival object
surv <- survival(surv, t = "time")
## Not run: autoplot(surv)

# (2) We can then compute state probabilities from the survival object
stprobs <- sim_stateprobs(surv)

# (3) Finally, we can use the state probabilities to compute QALYs and costs
## A dummy utility model to illustrate
utility_tbl <- stateval_tbl(
  data.table(state_id = 1:2,
             est = c(1, 1)
  ),
  dist = "fixed"
)
utilitymod <- create_StateVals(utility_tbl, 
                               hesim_data = hesim_dat,
                               n = 1)

## Instantiate Psm class and compute QALYs
psm <- Psm$new(utility_model = utilitymod)
psm$stateprobs_ <- stprobs
psm$sim_qalys()
psm$qalys_

State probability object

Description

An object of class stateprobs returned by sim_stateprobs() or from ⁠$sim_stateprobs()⁠ methods in model classes.

Components

A stateprobs object inherits from data.table and contains the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

grp_id

The subgroup ID.

state_id

The health state ID.

t

The time at which a state probability is computed.

prob

The probability of being in a given health state.

When simulating individual-level models, the patient_id column is not included as state probabilities are computed by averaging across patients.

In cohort models, the object also contains size and absorbing attributes. The size attribute is a numeric vector with the elements n_samples, n_strategies, n_patients, n_states, and n_times denoting the number of samples, treatment strategies, patients, health states, and times. The absorbing attribute is a numeric vector containing the absorbing health states (see the absorbing field of the CohortDtstmTrans class for more details).

Table to store state value parameters

Description

Create a table for storing parameter estimates used to simulate costs or utility in an economic model by treatment strategy, patient, health state, and (optionally) time interval.

Usage

stateval_tbl(
  tbl,
  dist = c("norm", "beta", "gamma", "lnorm", "unif", "fixed", "custom"),
  hesim_data = NULL,
  grp_var = NULL
)

Arguments

Details

tbl is a tabular object containing columns for treatment strategies (strategy_id), patients (patient_id), health states (state_id), and/or the start of time intervals (time_start). The table must contain at least one column named strategy_id, patient_id, or state_id, but does not need to contain all of them. Each row denotes a unique treatment strategy, patient, health state, and/or time interval pair. tbl may also contain a column with the name specified in grp_var (rather than patient_id) so that state values are assigned to groups of patients.

tbl must also contain columns summarizing the state values for each row, which depend on the probability distribution selected with dist. Available distributions include the normal (norm), beta (beta), gamma (gamma), lognormal (lnorm), and uniform (unif) distributions. In addition, the option fixed can be used if estimates are known with certainty and custom can be used if parameter values for a PSA have been previously sampled from an arbitrary probability distribution. The columns in tbl that must be included, by distribution, are:

norm

mean and sd

beta

mean and se or shape1 and shape2

gamma

mean and se, shape and rate, or shape and scale

lnorm

meanlog or sdlog

unif

min and max

fixed

est

custom

sample and value

Note that if dist = "custom", then tbl must include a column named sample (an integer vector denoting a unique random draw) and value (denoting the value of the randomly sampled parameter). In this case, there is a unique row in tbl for each random draw (sample) and each combination of strategies, patients, health states, and/or time intervals. Again, tbl must contain at least one column named strategy_id, patient_id (or grp_var), or state_id, but does not need to contain them all.

Value

An object of class stateval_tbl, which is a data.table of parameter values with attributes for dist and grp_var.

See Also

create_StateVals(), StateVals

Examples

strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3),
                       grp = c(1, 1, 2),
                       age = c(45, 50, 60),
                       female = c(0, 0, 1))
states <- data.frame(state_id = c(1, 2))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients,
                        states = states)

# Utility varies by health state and patient group
utility_tbl <- stateval_tbl(data.frame(state_id = rep(states$state_id, 2),
                                       grp = rep(rep(c(1, 2)), each = nrow(states)), 
                                       mean = c(.8, .7, .75, .55),
                                       se = c(.18, .12, .10, .06)),
                            dist = "beta",
                            grp_var = "grp")
print(utility_tbl)
utilmod <- create_StateVals(utility_tbl, n = 2, hesim_data = hesim_dat)

# Costs vary by treatment strategy
cost_tbl <- stateval_tbl(data.frame(strategy_id = strategies$strategy_id,
                                    mean = c(5000, 3000),
                                    se = c(200, 100)),
                         dist = "gamma")
print(cost_tbl)
costmod <- create_StateVals(cost_tbl, n = 2, hesim_data = hesim_dat)

Summarize costs and effectiveness

Description

Summarize costs and quality-adjusted life-years (QALYs) given output simulated from an economic model. The summary output is used to perform cost-effectiveness analysis with cea() and cea_pw().

Usage

summarize_ce(costs, qalys, by_grp = FALSE)

Arguments

Details

If mean costs and/or QALYs have already been computed (i.e., an average within a population), then there must be one observation for each discount rate (dr), PSA sample (sample), treatment strategy (strategy_id), and health state (state_id). Alternatively, there can be a column denoting a patient (patient_id), in which case outcomes will first be averaged across patients. A grp_id column can also be used so that outcomes are computed for each subgroup (if by_grp = TRUE); otherwise it is assumed that there is only one subgroup.

Value

An object of class ce.

Summary method for cost-effectiveness object

Description

Summarize a ce object by producing confidence intervals for quality-adjusted life-years (QALYs) and each cost category with summary.ce() and format for pretty printing with format.summary.ce().

Usage

## S3 method for class 'ce'
summary(object, prob = 0.95, labels = NULL, ...)

## S3 method for class 'summary.ce'
format(
  x,
  digits_qalys = 2,
  digits_costs = 0,
  dr_qalys = NULL,
  dr_costs = NULL,
  pivot_from = "strategy",
  drop_grp = TRUE,
  pretty_names = TRUE,
  ...
)

Arguments

Details

For an example, see IndivCtstm.

Value

summary.ce() returns an object of class summary.ce that is a tidy data.table with the following columns:

dr

The discount rate.

strategy

The treatment strategy.

grp

The patient subgroup.

type

Either "QALYs" or "Costs".

category

Category is always "QALYs" when type == "QALYs"; otherwise, it is the cost category.

estimate

The point estimate computed as the average across the PSA samples.

lower

The lower limit of the confidence interval.

upper

The upper limit of the confidence interval.

format.summary.ce() formats the table according to the arguments passed.

Summarize eval_rng object

Description

Summarize the model parameters randomly sampled for probabilistic sensitivity analysis with eval_rng().

Usage

## S3 method for class 'eval_rng'
summary(object, probs = c(0.025, 0.975), sep = "_", ...)

## S3 method for class 'eval_rng'
print(x, ...)

Arguments

Value

summary.eval_rng() returns a data.table::data.table with columns for (i) the name of the parameter (param), (ii) the mean of the parameter samples (mean), (iii) the standard deviation of the parameter samples (sd), and (iv) quantiles of the parameter samples corresponding to the probs argument. print.eval_rng() prints the output of summary.eval_rng() to the console.

See Also

See eval_rng() for an example.

Summarize parameter objects

Description

Summarize the coefficients of a parameter object by computing the mean, standard deviation, and quantiles for each model term. This is a convenient way to check whether a parameter object has been specified correctly and sampling distributions of the coefficients are as expected.

Usage

## S3 method for class 'params_lm'
summary(object, probs = c(0.025, 0.975), ...)

## S3 method for class 'params_mlogit'
summary(object, probs = c(0.025, 0.975), ...)

## S3 method for class 'params_mlogit_list'
summary(object, probs = c(0.025, 0.975), ...)

## S3 method for class 'params_surv'
summary(object, probs = c(0.025, 0.975), ...)

## S3 method for class 'params_surv_list'
summary(object, probs = c(0.025, 0.975), ...)

Arguments

Value

A data.table::data.table that always contains the following columns:

term

The regression term.

mean

The mean value of the regression term.

sd

The standard deviation of the values of the regression term.

In addition, the probs argument determines the quantiles that are computed. By default, the columns ⁠2.5%⁠ and ⁠97.5%⁠ are returned corresponding to the 2.5th and 97.5th percentiles.

Finally, the following columns may also be present:

parameter

The name of the parameter of interest. This is relevant for any parametric model in which the underlying probability distribution has multiple parameters. For instance, both params_surv and params_surv_list store regression coefficients that are used to model the underlying parameters of the survival distribution (e.g., shape and scale for a Weibull model). Similarly, there are two parameters (mean and sd) for params_lm objects.

model

The name of the statistical model. This is used for a params_surv_list object, where each list element represents a separate model. In a state transition model, each model is a unique health state transition and in a partitioned survival model, there is a separate model for each curve.

to

The health state that is being transitioned to. In params_mlogit and params_mlogit_list objects, there are coefficients for each health state that can be transitioned to.

from

The health state that is being transitions from. This is used for a params_mlogit_list objects where a different multinomial logistic regression is used for each state that can be transitioned from.

See Also

For examples, see the the underlying parameter object functions: params_lm(), params_surv(), params_surv_list(), params_mlogit(), and params_mlogit_list().

Summarize tparams_mean object

Description

The summary() method summarizes a tparams_mean object containing predicted means; summary statistics are computed for each combination of the ID variables. The print() method summarizes the object using summary.tparams_mean() and prints it to the console.

Usage

## S3 method for class 'tparams_mean'
summary(object, probs = c(0.025, 0.975), ...)

## S3 method for class 'tparams_mean'
print(x, ...)

Arguments

Value

A data.table with columns for (i) the ID variables, (ii) the mean of each parameter across parameter samples (mean), (iii) the standard deviation of the parameter samples (sd), and (iv) quantiles of the parameter samples corresponding to the probs argument.

See Also

See tparams_mean for an example use of the summary and print methods.

Summarize tparams_transprobs object

Description

The summary() method summarizes a tparams_transprobs object containing predicted transition probabilities; summary statistics are computed for each possible transition by the relevant ID variables.

Usage

## S3 method for class 'tparams_transprobs'
summary(object, probs = NULL, unflatten = FALSE, ...)

Arguments

Value

If unflatten = "FALSE" (the default), then a data.table::data.table is returned with columns for (i) the health state that is being transitioned from (from), (ii) the health state that is being transitioned to (to) (iii) the mean of each parameter across parameter samples (mean), (iv) the standard deviation of the parameter samples (sd), and (v) quantiles of the parameter samples corresponding to the probs argument.

If, on the other hand, unflatten = "TRUE", then the parameters are unflattened to form transition probability matrices; that is, the mean, sd, and quantile columns are (lists of) matrices.

In both cases, the ID variables are also returned as columns.

See Also

See tparams_transprobs for an example use of the summary method.

Summarize transition probability matrix

Description

Summarize a tpmatrix object storing transition probability matrices. Summary statistics are computed for each possible transition.

Usage

## S3 method for class 'tpmatrix'
summary(object, id = NULL, probs = NULL, unflatten = FALSE, ...)

Arguments

Value

If unflatten = "FALSE" (the default), then a data.table::data.table is returned with columns for (i) the health state that is being transitioned from (from), (ii) the health state that is being transitioned to (to) (iii) the mean of each parameter across parameter samples (mean), (iv) the standard deviation of the parameter samples (sd), and (v) quantiles of the parameter samples corresponding to the probs argument.

If, on the other hand, unflatten = "TRUE", then the parameters are unflattened to form transition probability matrices; that is, the mean, sd, and quantile columns are (lists of) matrices.

In both cases, if id is not NULL, then the ID variables are also returned as columns.

Examples

library("data.table")
hesim_dat <-  hesim_data(strategies = data.table(strategy_id = 1:2),
                                patients = data.table(patient_id = 1:3))
input_data <- expand(hesim_dat, by = c("strategies", "patients"))

# Summarize across all rows in "input_data"
p_12 <- ifelse(input_data$strategy_id == 1, .8, .6)
p <- tpmatrix(
  C, p_12,
  0, 1
)

## Summary where each column is a vector
summary(p)
summary(p, probs = c(.025, .975))

## Summary where each column is a matrix
ps <- summary(p, probs = .5, unflatten = TRUE)
ps
ps$mean

# Summarize by ID variables
tpmat_id <- tpmatrix_id(input_data, n_samples = 2) 
p_12 <- ifelse(tpmat_id$strategy_id == 1, .8, .6)
p <- tpmatrix(
  C, p_12,
  0, 1
)

## Summary where each column is a vector
summary(p, id = tpmat_id)

## Summary where each column is a matrix
ps <- summary(p, id = tpmat_id, unflatten = TRUE)
ps
ps$mean

Survival quantiles

Description

Compute quantiles from survival curves.

Usage

surv_quantile(x, probs = 0.5, t, surv_cols, by)

Arguments

Value

A data.table of quantiles of each survival curve in surv_cols by each group in by.

Examples

library("data.table")
t <- seq(0, 10, by = .01)
surv1 <- seq(1, .3, length.out = length(t))
surv2 <- seq(1, .2, length.out = length(t))
strategies <- c("Strategy 1", "Strategy 2")
surv <- data.table(strategy = rep(strategies, each = length(t)),
                   t = rep(t, 2), 
                   surv = c(surv1, surv2))
surv_quantile(surv, probs = c(.4, .5), t = "t",
              surv_cols = "surv", by = "strategy")

Survival object

Description

An object of class survival stores survival probabilities. It is typically returned by Psm$sim_survival() or PsmCurves$survival(); however, it can also be constructed "manually" from existing data using the survival() function as described below. The latter option is useful if survival modeling has been performed by an R package other than those that integrate with hesim ( currently flexsurv). In this case a simulation model can still be developed by using sim_stateprobs.survival() to compute simulated state probabilities and then simulating quality-adjusted life-years and costs in a typical fashion.

Usage

survival(
  data,
  sample = "sample",
  strategy_id = "strategy_id",
  patient_id = "patient_id",
  grp_id = "grp_id",
  curve = "curve",
  t = "t",
  survival = "survival"
)

Arguments

Value

An object of class survival that inherits from data.table and contains the following columns:

sample

A random sample from the PSA.

strategy_id

The treatment strategy ID.

patient_id

The patient ID.

grp_id

The subgroup ID.

curve

One of the N-1 survival curves in an N-state partitioned survival model. Each curve corresponds to unique endpoint.

t

The time at which a survival probability is computed.

survival

The probability of surviving to time t.

The object also contains a size attribute that contains the elements n_samples, n_strategies, n_patients, n_states, and n_times denoting the number of samples, treatment strategies, patients, health states, and times.

See Also

survival objects are returned by methods in the Psm and PsmCurves classes. An example in which a survival object is constructed "manually" (presumably from a preexisting survival model fit using software other than flexsurv) is provided in the documentation to sim_stateprobs.survival().

Time intervals

Description

Create a table of time intervals given a vector or data frame of unique times. This would typically be passed to id_attributes.

Usage

time_intervals(times)

Arguments

Value

An object of class time_intervals that inherits from data.table in the same format as time_intervals as described in id_attributes.

See Also

id_attributes

Examples

time_intervals(c(0, 3, 5))
time_intervals(data.frame(time_start = c(0, 3, 5),
                          time_cat = c("Time <= 3", "3 < Time <= 5", 
                                       "Time > 5")))

Transformed parameter object

Description

Objects prefixed by "tparams_" are lists containing transformed parameters used to simulate outcomes. The parameters have presumably already been transformed as a function of input data and consequently do not need to be used alongside input matrices. In other words, transformed parameters are parameters that have already been predicted as a function of covariates.

See Also

params

Predicted means

Description

Create a list containing means predicted from a statistical model.

Usage

tparams_mean(value, ...)

Arguments

Value

An object of class tparams_mean, which is a list containing value, n_samples, and the ID attributes passed to id_attributes.

Note

The tparams_mean() constructor would not normally be used by users; instead, a tparams_mean object is typically created automatically as part of the StateVals class with create_StateVals().

See Also

A tparams_mean object is a type of transformed parameter object and is a supported class type of the params field of the StateVals class. See the documentation for create_StateVals() and stateval_tbl() for examples of how to createStateVals objects. Predicted means can be summarized across parameter samples using summary.tparams_mean().

Examples

# Setup model
hesim_dat <- hesim_data(
  strategies = data.frame(strategy_id = c(1, 2)),
  patients = data.frame(patient_id = c(1, 2)),
  states = data.frame(
    state_id = c(1, 2, 3),
    state_name = c("state1", "state2", "state3")
  )
)

# Cost model
cost_tbl <- stateval_tbl(
  data.frame(strategy_id = hesim_dat$strategies$strategy_id,
             mean = c(5000, 3000),
             se = c(200, 100)
            ),
  dist = "gamma"
)
costmod <- create_StateVals(cost_tbl, n = 2, hesim_data = hesim_dat)

# The 'params' field of the `StateVals` class is a tparams_mean object
class(costmod$params)
costmod$params
summary(costmod$params)

Transition probabilities

Description

Create a list containing predicted transition probabilities at discrete times. Since the transition probabilities have presumably already been predicted based on covariate values, no input data is required for simulation. The class can be instantiated from either an array, a data.table, a data.frame, or a tpmatrix. This is the object in hesim used to specify the transition probabilities required to simulate Markov chains with the CohortDtstmTrans class.

Usage

tparams_transprobs(object, ...)

## S3 method for class 'array'
tparams_transprobs(
  object,
  tpmatrix_id = NULL,
  times = NULL,
  grp_id = NULL,
  patient_wt = NULL,
  ...
)

## S3 method for class 'data.table'
tparams_transprobs(object, ...)

## S3 method for class 'data.frame'
tparams_transprobs(object, ...)

## S3 method for class 'tpmatrix'
tparams_transprobs(object, tpmatrix_id, ...)

Arguments

Details

The format of object depends on its class:

array

Either a 3D or a 6D array is possible.

• If a 3D array, then each slice is a square transition probability matrix. In this case tpmatrix_id is required and each matrix slice corresponds to the same numbered row in tpmatrix_id. The number of matrix slices must equal the number of rows in tpmatrix_id.

• If a 6D array, then the dimensions of the array should be indexed as follows: 1st (sample), 2nd (strategy_id), 3rd (patient_id), 4th (time_id), 5th (rows of transition matrix), and 6th (columns of transition matrix). In other words, an index of ⁠[s, k, i, t]⁠ represents the transition matrix for the sth sample, kth treatment strategy, ith patient, and tth time interval.

data.table

Must contain the following:

• ID columns for the parameter sample (sample), treatment strategy (strategy_id), and patient (patient_id). If the number of time intervals is greater than 1 it must also contain the column time_start denoting the starting time of a time interval. A column patient_wt may also be used to denote the weight to apply to each patient.

• Columns for each element of the transition probability matrix. They should be prefixed with "prob_" and ordered rowwise. For example, the following columns would be used for a 2x2 transition probability matrix: prob_1 (1st row, 1st column), prob_2 (1st row, 2nd column), prob_3 (2nd row, 1st column), and prob_4 (2nd row, 2nd column).

data.frame

Same as data.table.

tpmatrix

An object of class tpmatrix.

A tparams_transprobs object is also instantiated when creating a cohort discrete time state transition model using define_model().

Value

An object of class tparams_transprobs, which is a list containing value and relevant ID attributes. The element value is an array of predicted transition probability matrices from the probability distribution of the underlying statistical model. Each matrix in value is a prediction for a sample, strategy_id, patient_id, and optionally time_id combination.

See Also

A tparams_transprobs object is used to store the "parameters" of the transition component of a cohort discrete time state transition model (cDTSTM). You can create such an object with CohortDtstmTran$new().

tpmatrix() and tpmatrix_id() provide a convenient way to construct a tparams_transprobs object in a flexible way. define_model() is, in turn, a convenient way to construct a tpmatrix object using mathematical expressions; in this case, an entire cDTSTM can be instantiated from a model definition using create_CohortDtstm.model_def(). Detailed examples are provided in vignette("markov-cohort") and vignette("markov-inhomogeneous-cohort")

The output of a tparams_transprobs object is rather verbose. It can be helpful to check the output by converting it to a data.table (containing both the ID variables and flattened transition probability matrices) with as.data.table.tparams_transprobs(). Transition probabilities can also be summarized (across parameter samples) using summary.tparams_transprobs().

Examples

hesim_dat <- hesim_data(strategies = data.frame(strategy_id = 1:2),
                        patients = data.frame(patient_id = 1:3))
input_data <- expand(hesim_dat, by = c("strategies", "patients"))    

# tpmatrix objects provide a convenient way to construct
# tparams_transprobs() objects
tpmat_id <- tpmatrix_id(input_data, n_samples = 2)      
p_12 <- runif(nrow(tpmat_id), .6, .7) + 
  .05 * (tpmat_id$strategy_id == 2)
tpmat <- tpmatrix(
  C, p_12,
  0, 1
)
tprobs <- tparams_transprobs(tpmat, tpmat_id)
names(tprobs) # Names of list elements

# Convert to data.table in wide format
as.data.table(tprobs)

# Convert to data.table in long format
as.data.table(tprobs, long = TRUE)

# Summary where each column is a vector
summary(tprobs)
summary(tprobs, probs = c(.025, .975))

# Summary where each column is a matrix
ps <- summary(tprobs, id = tpmat_id, unflatten = TRUE)
ps
ps$mean

Transition probability matrix

Description

tpmatrix() both defines and evaluates a transition probability matrix in which elements are expressions. It can be used within define_tparams() to create a transition probability matrix or directly to create a tparams_transprobs() object. These are, in turn, ultimately used to create a CohortDtstmTrans object for simulating health state transitions.

Usage

tpmatrix(..., complement = NULL, states = NULL, prefix = "", sep = "_")

Arguments

Details

A tpmatrix is a 2-dimensional tabular object that stores flattened square transition probability matrices in each row. Each transition probability matrix is filled rowwise. The complementary probability (equal to 1 minus the sum of the probabilities of all other elements in a row of a transition probability matrix) can be conveniently referred to as C or specified with the complement argument. There can only be one complement for each row in a transition probability matrix.

Value

Returns a tpmatrix object that inherits from data.table where each column is an element of the transition probability matrix with elements ordered rowwise.

See Also

A tpmatrix is useful because it provides a convenient way to construct a tparams_transprobs object, which is the object in hesim used to specify the transition probabilities required to simulate Markov chains with the CohortDtstmTrans class. See the tparams_transprobs documentation for more details.

The summary.tpmatrix() method can be used to summarize a tpmatrix across parameter samples.

Examples

p_12 <- c(.7, .6)
tpmatrix(
  C, p_12,
  0, 1
)

tpmatrix(
  C, p_12,
  C, 1
)

# Pass matrix
pmat <- matrix(c(.5, .5, .3, .7), byrow = TRUE, ncol = 4)
tpmatrix(pmat)

# Pass vectors and data frames
p1 <- data.frame(
  p_12 = c(.7, .6),
  p_13 = c(.1, .2)
)

p2 <- data.frame(
  p_21 = 0,
  p_22 = c(.4, .45),
  p_23 = c(.6, .55)
)

p3 <- data.frame(
  p_31 = c(0, 0),
  p_32 = c(0, 0),
  p_33 = c(1, 1)
)

tpmatrix(
  C, p1,
  p2,
  p3
)

# Use the 'complement' argument
pmat <- data.frame(s1_s1 = 0, s1_s2 = .5, s2_s1 = .3, s2_s2 = 0)
tpmatrix(pmat, complement = c("s1_s1", "s2_s2"))
tpmatrix(pmat, complement = c(1, 4)) # Can also pass integers

# Can control column names
tpmatrix(pmat, complement = c(1, 4),
         states = c("state1", "state2"), sep = ".")

Transition probability matrix IDs

Description

Creates ID variables for each row returned by tpmatrix(). This function is most conveniently used along with tpmatrix() to construct a tparams_transprobs() object.

Usage

tpmatrix_id(object, n_samples)

Arguments

Value

Returns a tpmatrix_id object that inherits from data.table with the same columns in object repeated n_samples times. That is, to facilitate creation of a tparams_transprobs() object, there is one row for each parameter sample, treatment strategy, patient, and optionally time interval.

See Also

tpmatrix(), tparams_transprobs(), expand.hesim_data()

Examples

strategies <- data.frame(strategy_id = c(1, 2))
patients <- data.frame(patient_id = seq(1, 3), age = c(65, 50, 75),
                        gender = c("Female", "Female", "Male"))
hesim_dat <- hesim_data(strategies = strategies,
                        patients = patients)
input_data <- expand(hesim_dat, by = c("strategies", "patients"))    
tpmatrix_id(input_data, n_samples = 2)                   

Names for elements of a transition probability matrix

Description

Create names for all elements of a transition probability matrix given names for the health states. This is useful for flattening a transition probability matrix (rowwise) into a vector and naming the resulting vector. The name of an element of the flattened vector representing a transition from the ith state to the jth state is of the form paste0(prefix, states[i], sep, states[j]).

Usage

tpmatrix_names(states, prefix = "p_", sep = "_")

Arguments

Value

A character vector containing a name for each element of the transition probability matrix encompassing all possible transitions.

See Also

See tpmatrix(), which uses tpmatrix_names() to name the columns of the returned object.

Examples

tpmatrix_names(LETTERS[1:4])
tpmatrix_names(LETTERS[1:4], prefix = "")
tpmatrix_names(LETTERS[1:4], prefix = "", sep = ".")

Generate variates for univariate distributions

Description

Generate variates for univariate distributions

Usage

uv_rng(n, params, rng_fun, mom_fun = NULL, names = NULL)

Parameterization of the Weibull distribution for network meta-analysis

Description

Density, distribution function, hazards, quantile function and random generation for the Weibull distribution when parameterized for network meta-analysis.

Usage

dweibullNMA(x, a0, a1 = FALSE, log = FALSE)

pweibullNMA(q, a0, a1, lower.tail = TRUE, log.p = FALSE)

qweibullNMA(p, a0, a1, lower.tail = TRUE, log.p = FALSE)

rweibullNMA(n, a0, a1)

hweibullNMA(n, a0, a1, log = FALSE)

HweibullNMA(n, a0, a1, log = FALSE)

rmst_weibullNMA(t, a0, a1, start = 0)

mean_weibullNMA(a0, a1)

Arguments

Value

dweibullNMA gives the density, pweibullNMA gives the distribution function, qweibullNMA gives the quantile function, rweibullNMA generates random deviates, HweibullNMA returns the cumulative hazard and hweibullNMA the hazard.

See Also

dweibull