| BalanceCheck | Balance Check for Multiple Covariates in Matched Observational Studies | 
| CrossMST | Covariate balance checking through the minimum spanning tree | 
| CrossNN | Covariate balance checking through the nearest neighbor graph | 
| getD | Get intermediate results for CrossNN | 
| getDk | Get intermediate results for CrossNN under k-NN | 
| getR1R2 | Get intermediate results for CrossMST | 
| smokingDist | The distance matrix of the smoking data |