Dear all,
I'd like to ask you about sample size calculation for a non-inferiority trial with POWER procedure.
What is the formula for calculating samplesize used in POWER procedure?
Sample SAS code is as follows:
PROC POWER;
TWOSAMPLEFREQ
TEST = PCHI
SIDES = U
ALPHA = .025
GROUPPROPORTIONS = (.75 .80)
NULLPROPORTIONDIFF=-.10
POWER = .8
Ntotal = .
;
RUN;
Thanks in advance,
Yasu
Hello Yasu!
One of the best books about it is "Chow, S.C.; Shao, J.; Wang, H. 2003. Sample Size Calculations in Clinical Research. Marcel Dekker. New York."
So your formula looks like:
n = (Zα/2+Zβ)2 * (p1(1-p1)+p2(1-p2)) / (p1-p2-NImargin)2
Zα/2=1.96
Zβ=0.84
better late than never
Andrei
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