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Accounting for Excess Zeros and Sample Selection in Poisson and Negative Binomial Regression Models

37 Pages Posted: 3 Nov 2008  

William H. Greene

New York University Stern School of Business

Date Written: March 1994

Abstract

We present several modifications of the Poisson and negative binomial models for count data to accommodate cases in which the number of zeros in the data exceed what would typically be predicted by either model. The excess zeros can masquerade as overdispersion. We present a new test procedure for distinguishing between zero inflation and overdispersion. We also develop a model for sample selection which is analogous to the Heckman style specification for continuous choice models. An application is presented to a data set on consumer loan behavior in which both of these phenomena are clearly present.

Suggested Citation

Greene, William H., Accounting for Excess Zeros and Sample Selection in Poisson and Negative Binomial Regression Models (March 1994). NYU Working Paper No. EC-94-10. Available at SSRN: https://ssrn.com/abstract=1293115

William H. Greene (Contact Author)

New York University Stern School of Business ( email )

44 West 4th Street
New York, NY NY 10012
United States
212-998-0876 (Phone)

HOME PAGE: http://people.stern.nyu.edu/wgreene

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