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Re: st: sample size calculation for binary repeated measures


From   "Austin Nichols" <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: sample size calculation for binary repeated measures
Date   Sat, 15 Sep 2007 11:21:54 -0400

Louis <LAPICELLA@popcouncil.org>:
I'm not really sure what your study design is, but "binary repeated
measures" sounds like a survival analysis, if by "binary" you mean an
outcome that can be coded 0 and 1 for "no failure yet" and "failure"
which implies you should check out
http://ideas.repec.org/p/boc/asug07/13.html

On 9/15/07, Apicella, Louis <LAPICELLA@popcouncil.org> wrote:
> 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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