Open AccessThe Importance and Role of Intracluster Correlations in Planning Cluster Trials
Author(s) -
John S. Preisser,
Beth A. Reboussin,
Eun Young Song,
Mark Wolfson
Publication year - 2007
Publication title -
epidemiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.901
H-Index - 173
eISSN - 1531-5487
pISSN - 1044-3983
DOI - 10.1097/ede.0b013e3181200199
Subject(s) - cluster (spacecraft) , sample size determination , intracluster medium , cluster randomised controlled trial , correlation , statistical power , research design , statistics , generalized estimating equation , sample (material) , estimation , psychology , intervention (counseling) , computer science , mathematics , physics , psychiatry , galaxy cluster , astrophysics , thermodynamics , programming language , management , economics , geometry , galaxy
There is increasing recognition of the critical role of intracluster correlations of health behavior outcomes in cluster intervention trials. This study examines the estimation, reporting, and use of intracluster correlations in planning cluster trials. We use an estimating equations approach to estimate the intracluster correlations corresponding to the multiple-time-point nested cross-sectional design. Sample size formulae incorporating 2 types of intracluster correlations are examined for the purpose of planning future trials. The traditional intracluster correlation is the correlation among individuals within the same community at a specific time point. A second type is the correlation among individuals within the same community at different time points. For a "time x condition" analysis of a pretest-posttest nested cross-sectional trial design, we show that statistical power considerations based upon a posttest-only design generally are not an adequate substitute for sample size calculations that incorporate both types of intracluster correlations. Estimation, reporting, and use of intracluster correlations are illustrated for several dichotomous measures related to underage drinking collected as part of a large nonrandomized trial to enforce underage drinking laws in the United States from 1998 to 2004.