Log-rank test

Summary

The log-rank test is a nonparametric hypothesis test that compares the survival distributions of two or more groups from right-censored data. At each event time it compares the observed number of events in a group with an expected number. The expected number is computed as if all groups had the same hazard function. Summing these differences and standardising gives a statistic that is approximately standard normal under the null hypothesis. It is the standard test for comparing Kaplan–Meier curves, and it is most efficient when the hazards of the groups are proportional.