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st: sample size calculation for binary repeated measures


From   "Apicella, Louis" <LAPICELLA@popcouncil.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: sample size calculation for binary repeated measures
Date   Sat, 15 Sep 2007 09:38:56 -0400

Hello Statalisters,

I am trying to determine the sample size for a binary repeated measures study in which we'll collect baseline data from two groups, intervention and control, then expose the intervention group, followed by collecting data twice more post-intervention from both groups.

I've been using this code to come up with sample sizes

sampsi .45 .55, sd1(.5) sd2(.5) power(.8) method(ancova) pre(1) post(2) r1(.5) r01(.5)

My question is that I have only proportions to work with and I'm not sure that sampsi is designed to use proportions when we specify sd1() and sd2().  I also feel that the variance should be closer to .1 for each sample but then my sample size is ridiculously small (n=8).  Essentially, what I want to be able to do is a comparison of the change in the intervention group to the change in the control group. Any ideas?

Thanks,

Lou.


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