Sample size – Survival analysis

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 = Z_α =

The standard normal deviate for β = Z_β =

A = (Z_α+Z_β)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	Events	Cumulative Event Rate
Group 1
Group 0
Total

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