One Arm Nonparametric Survival Sample Size and Power

Program Code

The program is written in JavaScript.


Brookmeyer R and Crowley, JJ. A confidence interval for the median survival time. Biometrics, 38, 29-41, 1982.

The formulas are based on the assumptions of uniform accrual over time, no loss to follow-up, exponentially distributed death times.  The tests and intervals are based on the large sample variance of the nonparametric estimate of cumulative hazard function.  For testing the median, a Brookmeyer-Crowley type test is assumed by comparing the cumulative hazard estimate at the M(null hypothesis median) to the -log(.5),

 T=(H(M0 )-(-log(.5))/SE(H(M0 )).

Input Items

The user is prompted for values to the following items. For items that have initial default values set, the values are given in parentheses.


The time specified for survival probability or median survival probabilities specified in the design must be less than the total of accrual and follow-up times.