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st: paired t-test and clustering

From   Bert Stover <>
Subject   st: paired t-test and clustering
Date   Wed, 12 May 2010 11:01:22 -0700 (PDT)

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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