THE 4-COUNTY STUDY OF CHILDHOOD-CANCER - CLUSTERS IN CONTEXT

Observations of childhood 'cancer clusters' in small communities in ce ntral California prompted us to examine the distribution of childhood cancer in communities throughout the region to see if the overall canc er rate or the distribution of 'cancer clusters' was unusual for agric ultural towns where pesticide exposure might be elevated. The distribu tion of rates was evaluated using a variety of methods: comparison of rates to the regional average, evaluation of the empirical observed ve rsus expected Poisson distribution of events, and multivariate modelli ng using Poisson regression. These analyses suggest that there were no previously undiscovered communities with excess rates, although the i ndex community which prompted the initial investigation does stand out as unusual. We discuss the impact of a range of forces of morbidity o n the likelihood of 'cancer clusters' and the distribution of observed and expected numbers of cancers in a population of locales.