Dear allstat-listers,
I have a variable T (which is time to failure) for a binary failure event. I
wish to test whether five groups, assumed to be homogenous, have the same
survivor function. So, I have tried using the logrank, the Wilcoxon
(Breslow-Gehan) and the Peto-Peto-Prentice tests in Stata as follows:
sts test group, logrank (assuming proportional hazards)
sts test group, wilcoxon (assuming hazards vary in ways other than
proportionally and censoring patterns are similar across groups)
sts test group, peto (assuming hazards vary in ways other than
proportionally and censoring patterns are different across groups)
All tests results indicate lack of equality (i.e. p-values <0.05). I was
wondering could that in part due to the sizeable groups I have
(about 120-200 patients per group), or is that real evidence of inequality
in survivor functions.
Many thanks for your help in advance.
Amani
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