A comparison of models for clustered binary outcomes: analysis of a designed immunology experiment

The lymphocyte proliferative assay (LPA) of immune competence was conducted on 52 subjects, with up to 36 processing conditions per subject, to evalua te whether samples could be shipped or stored overnight, rather than being processed on fresh blood as currently required. The LPA study resulted in c lustered binary data, with both cluster level and cluster-varying covariate s. Two modelling strategies for the analysis of such clustered binary data are through the cluster-specific and population-averaged approaches. Wherea s most research in this area has focused on the analysis of matched pairs d ata, in many situations, such as the LPA study, cluster sizes are naturally larger. Through considerations of interpretation and efficiency of these m odels when applied to large clusters, the mixed effect cluster-specific mod el was selected as most appropriate for the analysis of the LPA data. The m odel confirmed that the LPA response is significantly impaired in individua ls infected with the human immunodeficiency virus (HIV). The LPA response w as found to be significantly lower for shipped and overnight samples than f or fresh samples, and this effect was significantly stronger among HIV-infe cted individuals. Surprisingly, an anticoagulant effect was not detected.