Go to SWOG Web site   One Arm Nonparametric Survival Sample Size and Power


One Arm Survival is an interactive program for calculating either estimates of accrual or power for null and alternative survival functions based on either design specifications of survival probability or median survival. The test statistic for survival probability is assumed to be based on the non-parametric estimate of the survival distribution. For median survival, a Brookmeyer-Crowley like test assumed.  The program also gives large sample expected critical values for median survival (using Brookmeyer-Crowley) or survival probabilities.

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.  

Back to One Arm Non-Parametric Survival program.