A simple method for analysing overdispersion in clustered Poisson data.

A simple method is proposed for analysing grouped count data exhibiting overdispersion relative to a Poisson model. The method is similar to the approach suggested for the analysis of clustered binary data in Rao and Scott (1992). It requires no specific model for the overdispersion and it can be implemented easily using standard programs designed to handle independent Poisson counts, after a small amount of preprocessing.