Categorical Data Analysis Using The SAS® System, 2nd Edition

12.5. Overdispersion in Lower Respiratory Infection Example

Researchers studying the incidence of lower respiratory illness in infants took repeated observations of infants over one year. They studied 284 children and examined them every two weeks. Explanatory variables evaluated included passive smoking (one or more smokers in the household), socioeconomic status, and crowding. Refer to LaVange et al. (1994) for more information on the study and a discussion of the analysis of incidence densities. One outcome of interest was the total number of times, or counts, of lower respiratory infection recorded for the year. The strategy was to model these counts with Poisson regression. However, it is reasonable to expect that the children experiencing ...