Score Test for Zero Inflated Generalized Poisson Regression Model

Abstract

In certain applications involving count data, it is sometimes found that zeros are observed with a frequency significantly higher (lower) than predicted by the assumed model. Examples of such applications are cited in the literature from engineering, manufacturing, economics, public health, epidemiology, psychology, sociology, political science, agriculture, road safety, species abundance, use of recreational facilities, horticulture and criminology. In this article, a zero adjusted generalized Poisson distribution is studied and a score test is developed, with and without covariates, to determine whether such an adjustment is necessary. Examples, with and without covariates, are provided to illustrate the results.

Key Words:

• Zero-inflated model
• Generalized Poisson distribution
• Score test
• Covariate

Acknowledgment

The authors are thankful to the referee for some useful suggestions which enhanced the presentation.