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Re: st: sample size calculation for binary repeated measures


From   Joseph Coveney <jcoveney@bigplanet.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: sample size calculation for binary repeated measures
Date   Sun, 16 Sep 2007 20:13:29 -0700

Louis Apicella wrote:

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?

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