Marginal analysis of multiple outcomes with informative cluster size
Periodontal disease is a serious infection of the gums and the bones surrounding the teeth. In Veterans Affairs Dental Longitudinal Study (VADLS), the relationships between periodontal disease and other health and socioeconomic conditions are of interest. To determine whether or not a patient has periodontal disease, multiple clinical measurements (clinical attachment loss, alveolar bone loss, tooth mobility) are taken at the tooth-level. However, a universal definition for periodontal disease does not exist and researchers often create a composite outcome from these measurements or analyze each outcome separately. Moreover, patients have varying number of teeth, with those that are more prone to the disease having fewer teeth compared to those with good oral health. Such dependence between the outcome of interest and cluster size (number of teeth) is called informative cluster size, and results obtained from fitting conventional marginal models can be biased. In this talk, I will introduce a novel method to jointly analyze multiple correlated outcomes for clustered data with informative cluster size using the class of generalized estimating equations (GEE) with cluster-specific weights. Using the data from VADLS, I will compare the results obtained from the proposed multivariate outcome cluster-weighted GEE to those from the conventional unweighted GEE. Finally, I will discuss a few other research settings where data may exhibit informative cluster size.