Find statistical considerations for a study
where the outcome is a time to failure

Significance Level (usually 0.05) -- sided (usually 2 sided).

Accrual interval*

Follow-up interval

Median time to failure in group with smallest time to failure, in

Enter two of the following three values and the remaining value will be calculated.

  1. Power, usually .8 or .9.
  2. Total number of patients.
  3. Minimal detectable hazard ratio or ratio of median survival (>1)

This page is a modified version of a page made by:

David A. Schoenfeld, Ph.D.

*Accrual time: The time it takes to enroll all patients, when the follow-up time is fixed this can be set to 0. It needs to be specified when all participants are followed until the study stops, i.e. the accrural interval adds observation time.

This method does not take attrition into consideration.

The program "Power and Precision" can handle drop-outs and can be purchased from