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Re: st: paired t-test and clustering


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: paired t-test and clustering
Date   Wed, 12 May 2010 16:31:24 -0400

standard errors.  Assuming that you have computed the paired
differences already and stored them a variable called diff),  the
following code will give you the appropriate t-test:

reg diff, cluster(familyID)

Adding family and person-level variables  as covariates might also be
informative.

Steve

On Wed, May 12, 2010 at 2:01 PM, Bert Stover <bstover@u.washington.edu> wrote:
> My question concerns paired t-test and clustering.
> I would like to determine if a mean activity score before intervention is different from the mean activity score after intervention. I have used a paired t-test using the pre- and post-intervention activity score from the same person. The activity scores are normally distributed.
>
> Several reviewers have suggested that my estimates are too optimistic and incorrectly find a significant difference between the pre and post means because I have not controlled for clustering (correlated data) due to including multiple members from families. Measurements from multiple subjects from a family may be similar and not be considered independent observations. I have 300 subjects from 90 families.
>
> Does using the individual as their own control in the paired t-test avoid the bias due to clustering? If not, what methods are available to compare the per- and post-intervention means while adjusting for clustering?
>
> Thank You Bert Stover
>
>
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-- 
Steven Samuels
sjsamuels@gmail.com
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USA
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