A score test for zero-inflation in multilevel count data

The zero-inflated Poisson regression (ZIP) in many situations is appropriate for analyzing multilevel correlated count data with excess zeros. In this paper, a score test for assessing ZIP regression against Poisson regression in multilevel count data with excess zeros is developed. The sampling distribution and power of the score statistic test is evaluated using a simulation study. The results show that under a wide range of conditions, the score statistic performs satisfactorily. Finally, the use of the score test is illustrated on DMFT index data of children 7-8 years old.