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st: sample size calculation

From   Ricardo Ovaldia <>
Subject   st: sample size calculation
Date   Wed, 29 Sep 2004 11:04:04 -0700 (PDT)

Dear all,

In an article that I am reading the authors write:

"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)" 

They claim that they did this and all analysis using
Stata 5.0. They do not provide group means or any
discriptive statistics on which the sample size was

Can someone please tell me how this could have been
done. And is there a program to do this in Stata?

Thank you in advance,

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