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st: Computing effect size for a clustered randomized control trial


From   Joe McCrary <joe.mccrary@gmail.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: Computing effect size for a clustered randomized control trial
Date   Mon, 3 May 2010 17:23:12 -0600

I am designing a randomized control trial, where we are going to
select about 12 students per classroom and randomize them into 3
groups, a control and 2 treatment groups. Is there a way I can compute
the number of classrooms needed for the study using the following
criteria:

Desired power=0.8
Estimated effect size = 0.2
alpha = 0.0167
1 pre-test measure
1 post-test measure
approx correlation between the two measures = 0.25

--
Joe McCrary
Senior Research Associate
WestEd-Atlanta
260 Peachtree St., Suite 2200
Atlanta, GA 30303

ph: 541-782-8626
fax: 404-393-3797

Skype: joe.mccrary
Google talk; joe.mccrary
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