We plan to conduct a study for comparing the survival rate between three different types of surgery for total knee arthroplasty. Thus, the sample size for the study should be estimated.



But, we only could calculate the sample size for two groups by log-rank test in Stata as follow:

1、Sample size for censored design with survival probabilities surv1 = 0.3 and surv2 = 0.4:

power logrank .3 .4

2、or，

Same as above, specified as surv1 = 0.3 and hazard ratio of 0.76 :

power logrank .3, hratio(.76)



Notably, how to calculated the sample size for three groups (or >2 groups) by log-rank test in Stata?



Thanks!