[R] log-rank when var < 5 and power

From: Wittner, Ben <Wittner.Ben_at_mgh.harvard.edu>
Date: Sat 30 Apr 2005 - 08:01:35 EST


I would like to determine whether there's a difference between survival data for two groups.

I have been using the survival package and survdiff() with rho=0 and rho=1. Survdiff() with rho=0 is a non-continuity-corrected version of the log-rank test set forth in "Fundamentals of Biostatistics" by Bernard Rosner. On page 722 of the 5th edition, Rosner states, "This test should be used only if Var_LR >= 5." For my data with rho=0 or rho=1, survdiff()$var[1,1] is much less than 5.

Can anyone suggest what to do in this case?

Also, can anyone suggest a reference or software for doing power calculations regarding tests for difference between survival data for two groups.

Thanks very much.

-Ben



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