Sample size determination for two sample survival rank tests (annual survival probabilities)

Brief description

This web application is an implementation of sample size determination methods for the log-rank test, the Gehan rank test, and the Tarone–Ware rank test (Lakatos, 1988), assuming the proportional hazards assumption holds. This app is implemented in JavaScript, and it does not collect any information from user input.

Survival time, Accural time, Follow-up time: You should unify time unit (year or month).

Allcation ratio: When the ratio, $r \gt 1$, sample size of test group is larger than of standard group ($n_{\mathrm{test}} = r n_{\mathrm{std}}$). For instance, when $r = 2$, $n_{\mathrm{test}} = 2 n_{\mathrm{std}}$.






  1. Lakatos E. Sample sizes based on the log-rank statistic in complex clinical trials. Biometrics 1988;44:229–241.
  2. Lakatos E, Lan KK. A comparison of sample size methods for the logrank statistic. Statistics in Medicine 1992;11(2):179–191.

Update history

  • 2019/7/31 Fixed: almost exact sample sizes according to the allocation ratio can be calculated (Thanks to Dr. Masayuki Yamada)
  • 2017/12/1 Added: English translation
  • 2015/3/5 Fixed: allocation ratio is now handled correctly (Thanks to Dr. Masayuki Yamada)
  • 2012/12/7 Added: outputs includes expected event numbers (Thanks to Junki MIZUSAWA)
  • 2012/3/26 Added: test release

To cite this page

  • Nagashima K. A sample size determination tool for two sample survival rank tests [Internet]. 2012 Mar 26 [cited 20XX YYY ZZ]; Available from: