Re: st: Computing effect size for a clustered randomized control trial

[Jeph Herrin <junk@spandrel.net>]

you can try -findit sampclus-

but whatever method you use, you will need an estimate of the
intraclass correlation.

hth,
Jeph

Joe McCrary wrote:
> 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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