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Re: st: RE: sample size calculation


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: sample size calculation
Date   Wed, 29 Sep 2004 15:45:03 -0500

At 12:31 PM 9/29/2004 -0700, Ricardo Ovaldia wrote:
--- "Lin, Chung-Tung" <Chung-Tung.Lin@cfsan.fda.gov>
wrote:

> you may want to look at the sampsi command for
> details.

Thank you Jordan Lin, but -sampsi- requires that you
specify means and SD, which I do not have and is the
reason that I asked the question.
Actually, you do, don't you? The original problem was

"it was decided a priori to include a minimum quantity
of mother, which could allow the statistical power
(alpha=0.05, beta=0.80) for assessing
differences of 10% in nicotine concentration by group
with an expected standard deviation of 15 ng/mg. These
criteria led to the analysis of 150 mothers (50 for
each of the 3 groups)"

So, for the SDs, you use 15. But, I am not sure how you fill in the rest, especially since they came up with 3 groups, not 2. Even if it was 2 groups, I am not clear on how you would be expected to enter the means (take logs first or something?) In any event, I think the necessary information may be there, but I'm not sure either on what to do with it!

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Richard Williams, Notre Dame Dept of Sociology
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