Estimation and testing of binomial and beta-binomial regression models with and without zero inflation

Abstract

We present new Stata commands for carrying out several regression commands suitable for binomial outcomes. The zib command extends Stata’s binreg command to allow zero inflation. The betabin command fits binomial regression models allowing for beta overdispersion, and the zibbin command fits a beta-binomial regression model with zero inflation. All the new commands allow the specification of links within the glm command’s collection for both outcome and zero inflation. The zero-inflated commands optionally calculate a Vuong test comparing the zero-inflated model with the nonzero-inflated model, and the zibbin command optionally includes a likelihood-ratio test of the overdispersion parameter.