Two calculators for two-group survival analysis.

Calculator 1: Number of events, given relative hazard.

Instructions: Enter parameters in the red cells. Answers will appear in blue below.

 α (two-tailed) = Threshold probability for rejecting the null hypothesis. Type I error rate. β = Probability of failing to reject the null hypothesis under the alternative hypothesis. Type II error rate. q1 = Proportion of subjects that are in Group 1 (exposed) q0 = 0.700 Proportion of subjects that are in Group 0 (unexposed); 1-q1 RH = Relative hazard (Group 1/Group 0)

The standard normal deviate for α = Zα =

The standard normal deviate for β = Zβ =

A = (Zα+Zβ)2 =

B = (log(RH))2q0q1 =

Total events needed = A/B =

Calculator 2: Sample size, given number of events.

This calculator will calculate the number of subjects needed in each group to achieve the number of events calculated above.

q1 = 0.300

q0 = 0.700

RH = 0.667

Total events =

Note: If you change the default values for EITHER BER0 or ST0 below, the calculator will automatically update the other parameter accordingly.

 BER0 = Baseline Event Rate (events/unit time) for Group 0 ST0 = Median survival time in Group 0 CR = Censoring rate - censored/unit time (assumed equal for both groups) FU = Planned average length of follow-up, in time units
N EventsCumulative Event Rate
Group 1
Group 0
Total

Reference: Schoenfeld DA. Sample-size formula for the proportional-hazards regression model. Biometrics 1983;39:499-503.