PROC POWER TWOSAMPLESURVIVAL

[Alroz]

Hello,

I am trying to estimate a sample size for the log rank test comparing two different treatment arms.

The study will have a three year followup when the effect of the treatment will change after each year.

the input I am using is:

proc power;

   twosamplesurvival test=logrank

      Alpha = 0.05

      curve("trt1") = 1:0.65 2:0.53625 3:0.489328125

        curve("trt2") = (1 to 3 by 1):(0.82 0.7462 0.712621)

      groupsurvival = "trt1" | "trt2"

      accrualtime = 2

      Totaltime = 3

        groupmedlosstimes = 10 | 10

        groupweights = (1 2)

        power = 0.90

      EVENTSTOTAL=.

;

Run;

This program designs a piecewise linear effect. Can I choose an ascending or descending linear effect?

Also, I want to define a piecewise exponential?

And last, Can I define the effect in hazard ratio terms and not survival curve but with a changing hazard ratio over time?

Thank you!