ABSTRACT
This chapter describes some methods of exploratory data analysis whose aim is to check whether or not the various assumptions of homogeneity common in epidemic theory are indeed reasonable. It addresses questions concerned with immunity or heterogeneity in disease spread due to differences in sex, age or group behaviour. The chapter explores the limited extent to which disease incidence data alone can throw light on the immunity status of the community. Attention is turned to the analysis of data from a single epidemic in a somewhat larger community, possibly a community of households. Under the assumption that everyone in the community was susceptible to the disease one may be led to conclude that this disease is only mildly infectious. A series of epidemics of a certain disease in the one community provides greater scope for exploring the question of immunity. The immunity status of individuals is probably best assessed by laboratory tests on blood, saliva or excreta samples.
