Re: [R] Help re zinb model

From: Achim Zeileis <>
Date: Thu 04 Jan 2007 - 10:41:55 GMT

On Thu, 4 Jan 2007, wrote:

> Remember that -2 * the difference in the likelihoods between the two
> models is asymptotically chi-squared distributed, with degrees of
> freedom equal to the difference in number of parameters between the
> models. So you can just calculate that for your preferred and null
> models, then use the pchisq function
> to test significance. Get the likelihoods from obj$maxlike.

The function lrtest() in package "lmtest" offers a flexible implementation of this which works for fitted models that provide a logLik() method. The zicounts() implementation does not, but zeroinfl() in package "pscl". E.g. you can do:

data("teeth", package = "zicounts")
fm1 <- zeroinfl(dmft ~ gender + age | gender + age, data = teeth,

   dist = "negbin")
fm2 <- zeroinfl(dmft ~ 1, data = teeth, dist = "negbin") summary(fm2)

lrtest(fm1, fm2)

Z mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Thu Jan 04 21:47:29 2007

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