Grouped GEE Analysis for Longitudinal Data
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Generalized estimating equation (GEE) is widely adopted for regression modeling for longitudinal data, taking account of potential correlations within the same subjects. Although the standard GEE assumes common regression coefficients among all the subjects, such assumption is not realistic when there are potential heterogeneity in regression coefficients among subjects. In this paper, we develop a flexible and interpretable approach, called grouped GEE analysis, to modeling longitudinal data with allowing heterogeneity in regression coefficients. The proposed method assumes that the subjects are divided into a finite number of groups and subjects within the same group share the same regression coefficient. We provide a simple algorithm for grouping subjects and estimating the regression coefficients simultaneously, and show asymptotic properties of the proposed estimator. The number of groups can be determined by an information criteria using quasi-likelihood. We demonstrate the proposed method through simulation studies and an application to a real dataset.
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