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Log-Rank Test Sample Size Calculator

Free

Calculate the sample size needed to compare survival curves between two groups using the log-rank test.

Study Parameters
Results

Required Sample Size

785

Group 1: 393 | Group 2: 392

Achieved Power

80.0%

Effect Size

0.357

Method: Log-Rank Test (Schoenfeld 1983)
Events required247
Overall event probability0.350
log(HR)0.357
Allocation ratio1:1
  • •Proportional hazards assumption
  • •Exponential (constant hazard) within each group
  • •Two-sided hypothesis test
  • •Allocation ratio k = 1
  • •Dropout rate: 10%
Formula
D = (z_{alpha/2} + z_beta)^2 / [p1 * p2 * (log HR)^2]; N = D / P(event)
References
  1. Schoenfeld DA (1983). Sample-size formula for the proportional-hazards regression model. Biometrics, 39(2), 499-503.
  2. Freedman LS (1982). Tables of the number of patients required in clinical trials using the logrank test. Statistics in Medicine, 1(2), 121-129.