document: Score tests for zero-inflated Poisson models In many situations count data have a large proportion of zeros and the zero-inflated Poisson regression -LRB- ZIP -RRB- model may be appropriate . A simple score test for zero-inflation , comparing the ZIP model with a constant proportion of excess zeros to a standard Poisson regression model , was given by van den Broek -LRB- 1995 -RRB- . We extend this test to the more general situation where the zero probability is allowed to depend on covariates . The performance of this test is evaluated using a simulation study . To identify potentially important covariates in the zero-inflation model a composite test is proposed . The use of the general score test and the composite procedure is illustrated on two examples from the literature . The composite score test is found to suggest appropriate models
doc_bio_tags: B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B O O O O O O O O O O B O O O O O O B O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
extractive_keyphrases: count data score tests zero probability covariates excess zeros simulation composite test
abstractive_keyphrases: zero-inflated poisson regression model