Suppose I have 1000 patients enrolled in a trial (assuming 1:1 randomization to Treatment and Control arms), and my objective is to estimate the number of events (e.g., overall survival) needed to have a test of power at least 0.8 under the assumption of alpha=0.05. I wonder if there are formulas there to use, and/or R package that performs such power/sample size analyses. Thank you!
There are ways of calculating this, but not implemented in R as far as I know. A good read would be Therenay & Grambsch's book (the reference for the survival package), chapter 3.3 "Sample size". If you don't have access to this book, it references the following 3 papers:
- D. A. Schoenfeld. Sample-size formula for the proportional-hazards regression model. Biometries, 39:499-503, 1983.
- D. Schoenfeld. The asymptotic properties of nonparametrie tests for comparing survival distributions. Biometrika, 68:316-319, 1981.
- D. Berstein and S. W. Lagakos. SampIe size and power determination for stratified clinical trials. J Stat. Comput. Simul., 8:65-73, 1978.