Sample size calculator

Input and calculation

Alpha two-sided

/ =

Power

Sample size per group

Sample size in group 2

Allocation ratio n₁:n₂ :

Drop-out rate

Press the Calculate button to calculate the sample size.

Options

Calculate
Sample size
Power (output decimal places: )

Advanced
Unequal sample sizes
Account for drop-outs
Bonferroni correction

Total number of events

Number of events for a two-sample logrank test

The required number of events and the power for the logrank test are calculated according to Schoenfeld's formula, see [Schoenfeld, D. (1981). The asymptotic properties of nonparametric tests for comparing survival distributions. Biometrika, 68(1), 316-319.] and [Schoenfeld, D. A. (1983). Sample-size formula for the proportional-hazards regression model. Biometrics, 499-503.]

x-year survival 1

x-year survival 2

Hazard ratio

Specific options
Calculate hazard ratio from x-year survival