We present new Stata commands for estimating several regression models suitable for analyzing overdispersed count outcomes. The nbregp command nests the dispersion(constant) and dispersion(mean) versions of Stata’s nbreg command in a model for negative binomial(p) regression. The zignbreg command extends Stata’s gnbreg command for zero inflation, and the zinbregp command fits a negative binomial(p) regression model with zero inflation. The new commands for zero-inflated models allow specification of links within the glm command’s collection for the Bernoulli model of zero inflation. These commands will optionally calculate a Vuong test, which compares the zero-inflated model with the nonzeroinflated model.


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