Score Tests for Extra-Zero Models in Zero-Inflated Negative Binomial Models

Authors: Jansakul, N.¹; Hinde, John²

Source: Communications in Statistics: Simulation and Computation, Volume 38, Number 1, November 2008 , pp. 92-108(17)

Publisher: Taylor and Francis Ltd

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Abstract:

When overdispersion is present in count data, a negative binomial (NB) model is commonly used in place of the standard Poisson model. However, the model is sometimes not adequate because of the occurrence of excess zeros and a zero-inflated negative binomial (ZNB) model may be more appropriate. This article proposes a general score test statistic for comparing a ZNB regression model to the NB model and the test is extended to a composite score test. Simulation results indicate that the test performs reasonably well and has a sampling distribution under the null hypothesis (NB model) approximated by the usual χ2 distribution. Use of the test is illustrated on a set of apple shoot propagation data. The composite score test is found to indicate suitable models.

Keywords: Count data; Overdispersion; Score test; Zero-inflation

Document Type: Research article

DOI: http://dx.doi.org/10.1080/03610910802421632

Affiliations: 1: Department of Mathematics, Prince of Songkla University, Songkhla, Thailand 2: Department of Mathematics, National University of Ireland, Galway, Ireland

Publication date: 2008-11-01