A Note on Collapsibility in DAG Models of Contingency Tables
Sung-Ho Kim, SUNG‐HO KIM, SEONG‐HO KIM, SEONG‐HO KIM · Scandinavian Journal of Statistics · 2006
Abstract. Necessary and sufficient conditions for collapsibility of a directed acyclic graph (DAG) model for a contingency table are derived. By applying the conditions, we can easily check collapsibility over any variable in a given model either by using the joint probability distribution or by using the graph of the model structure. It is shown that collapsibility over a set of variables can be checked in a sequential manner. Furthermore, a DAG is compared with its moral graph in the context of collapsibility.