strmst2 and strmst2pw: New commands to compare survival curves using the restricted mean survival time

Abstract

We present strmst2, a new command to implement k-sample comparisons using the restricted mean survival time (RMST) as the summary measure of the survival-time distribution. Unlike model-based summary measures such as the hazard ratio, the validity of which relies on the adequacy of the proportional hazards assumption, the measures based on the RMST (that is, the difference in RMST, the ratio of RMST, and the ratio of the restricted mean time lost) provide more robust and clinically interpretable results about the between-group differences. strmst2 performs analysis of covariance-type adjusted analyses for k-sample comparisons as well as the corresponding unadjusted analyses. Pairwise comparisons for the adjusted analyses are summarized using the new postestimation command strmst2pw. We briefly describe the issues of the hazard ratio, introduce details of the method for the RMST, and then illustrate how to use the new commands.