Education And Debate Statistics Notes

The logrank test

BMJ 2004; 328 doi: (Published 29 April 2004) Cite this as: BMJ 2004;328:1073
  1. J Martin Bland, professor of health statistics1,
  2. Douglas G Altman, professor of statistics in medicine2
  1. 1Department of Health Sciences, University of York, York YO10 5DD
  2. 2Cancer Research UK/NHS Centre for Statistics in Medicine, Institute of Health Sciences, Oxford OX3 7LF
  1. Correspondence to: Professor Bland

    We often wish to compare the survival experience of two (or more) groups of individuals. For example, the table shows survival times of 51 adult patients with recurrent malignant gliomas1 tabulated by type of tumour and indicating whether the patient had died or was still alive at analysis—that is, their survival time was censored.2 As the figure shows, the survival curves differ, but is this sufficient to conclude that in the population patients with anaplastic astrocytoma have worse survival than patients with glioblastoma?

    View this table:

    Weeks to death or censoring in 51 adults with recurrent gliomas1 (A=astrocytoma, G=glioblastoma)

    Fig 1

    Survival curves for women with glioma by diagnosis

    We could compute survival curves3 for each group and compare the proportions surviving at any specific time. The weakness of this approach is that it does not provide a comparison of the total survival experience of the two groups, but rather gives a comparison at some arbitrary time point(s). In the figure the difference in survival is greater at some times than others and eventually becomes …

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