I am trying to calculate the required sample size for a future study.
Specifically, the goal is to compare two treatments based on their survival. The Cox model will be used, and along with the treatment indicator (0/1) there will be also some other covariates, both binary and non-binary.
The big problem, as always, is that there is no data available. I found the function powerEpi in R, but this is only for two covariates in the model. Some other functions in the same package (powerSurvEpi) need actual/pilot data for the calculation.
Can somebody propose a function/software/formula for this case ?