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  "body": "\n## Summary\n\nThe log-rank test is a nonparametric [[hypothesis test|087P03NEND]] that compares the survival distributions of two or more groups from right-[[censored|MY8ZZP84NP]] data.\nAt each event time it compares the observed number of events in a group with an expected number.\nThe expected number is computed as if all groups had the same [[hazard function|Y959NKQ3XW]].\nSumming these differences and standardising gives a statistic that is approximately standard normal under the null hypothesis.\nIt is the standard test for comparing [[Kaplan–Meier|B7AJ8RWZRC]] curves, and it is most efficient when the hazards of the groups are proportional.\n\n## Explanations\n\n### L1 human\n\nTwo groups of patients get different treatments, and we record when each patient has a relapse.\nEach time someone relapses, we look at how many patients of each group were still at risk.\nFrom this we compute how many of these relapses we would expect in group 1 if the treatments were equally good.\nThe test adds up \"observed minus expected\" over all relapse times.\nA large total, compared with its natural spread, suggests that the treatments really differ.\n",
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