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A Mixed Model‐Based Variance Estimator for Marginal Model Analyses of Cluster Randomized Trials
Author(s) -
Braun Thomas M.
Publication year - 2007
Publication title -
biometrical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.108
H-Index - 63
eISSN - 1521-4036
pISSN - 0323-3847
DOI - 10.1002/bimj.200510280
Subject(s) - estimator , gee , statistics , mathematics , marginal model , generalized estimating equation , consistent estimator , crts , estimating equations , bootstrapping (finance) , quasi likelihood , econometrics , variance (accounting) , standard error , regression analysis , count data , minimum variance unbiased estimator , computer science , computer graphics (images) , poisson distribution , accounting , business
Generalized estimating equations (GEE) are used in the analysis of cluster randomized trials (CRTs) because: 1) the resulting intervention effect estimate has the desired marginal or population‐averaged interpretation, and 2) most statistical packages contain programs for GEE. However, GEE tends to underestimate the standard error of the intervention effect estimate in CRTs. In contrast, penalized quasi‐likelihood (PQL) estimates the standard error of the intervention effect in CRTs much better than GEE but is used less frequently because: 1) it generates an intervention effect estimate with a conditional, or cluster‐specific, interpretation, and 2) PQL is not a part of most statistical packages. We propose taking the variance estimator from PQL and re‐expressing it as a sandwich‐type estimator that could be easily incorporated into existing GEE packages, thereby making GEE useful for the analysis of CRTs. Using numerical examples and data from an actual CRT, we compare the performance of this variance estimator to others proposed in the literature, and we find that our variance estimator performs as well as or better than its competitors. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)