Analysis of Zero-Inflated Poisson Data Incorporating Extent of Exposure

When analyzing Poisson count data sometimes a high frequency of extra zeros is observed. The Zero-Inflated Poisson (ZIP) model is a popular approach to handle zero-inflation. In this paper we generalize the ZIP model and its regression counterpart to accommodate the extent of individual exposure. Empirical evidence drawn from an occupational injury data set confirms that the incorporation of exposure information can exert a substantial impact on the model fit. Tests for zero-inflation are also considered. Their finite sample properties are examined in a Monte Carlo study.