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st: applying sampsi: sub-groups

From   Michael McCulloch <>
To   Statalist <>
Subject   st: applying sampsi: sub-groups
Date   Wed, 6 Feb 2008 14:08:37 -0800

I am applying sampsi to a project design, and am puzzled by a question which perhaps one of the list members may have an opinion.

In my study design, subjects are randomized to one of two groups, treatment and control. Treatment group receives the new intervention, and control groups receives standard care.

My question is the following: after random allocation, within the treatment group subjects will be assigned to one of three treatment doses of the same treatment, depending on a differential diagnosis. In practice, in estimating sample size requirements, would one consider the three sub-groups as distinct groups, or aggregate them all into the treatment group?

Thank you.


Best wishes,
Michael McCulloch

Pine Street Foundation
124 Pine St., San Anselmo, CA 94960-2674
Tel: (415) 407-1357
Fax: (415) 485-1065
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