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st: Optimal ratio of sample sizes in two sample t test

From   Douglas McKee <>
Subject   st: Optimal ratio of sample sizes in two sample t test
Date   Mon, 7 Jan 2013 14:50:40 -0500

Hi all,

Suppose I'm trying to choose the sample sizes for a study where I have two populations that are equally costly to sample.  If I know the standard deviations of each group, I can use sampsi to compute the n's when I specify effect size, alpha and desired power.  But suppose one sample has a low variance and the other has a high variance.  Doesn't this mean I should sample more from the high variance group?  Is there a way to make Stata tell me the optimal n1/n2 ratio?  Or should I write a wrapper around sampsi that tries a variety of ratios and tells me which one yields the smallest n1+n2?

Thanks very much,

Douglas McKee
Associate Chair and Lecturer, Economics
Lecturer, School of Medicine
Yale University
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