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

[Wittner, Ben]

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