The implications of differential clustering for analysis of binary outcomes

Introduction Clustering may arise in clinical trials due to either randomisation in a cluster randomised trial, or due to treatment. Examples of treatment related clustering are activity classes or therapeutic support groups, where patients are nested in therapy group, or talking and physical therapies where patients are nested by therapist. In either setting the clustering effect may differ between treatments. In this presentation we consider the implications of a differential clustering effect for analysis of binary outcome measures.