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st: Count data problems


From   Claire <bildee@blueyonder.co.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Count data problems
Date   Tue, 20 Aug 2002 09:01:00 +0100

Hello,

I have a large database of count data, 95% zeros & overdispersion (variance
25 x larger than the mean) - I have tried poisson, nbreg, zinb & zip with
the Vuong test.  The problem is that the results for the zinb, which the
Vuong test shows is preferable over the nbreg, are poor in that very few
explanatory variables are significant.  Is there any other way to account
for excess zeros/overdispersion using nbreg rather than zinb?  The reason I
can't accept my current nbreg model is that the scaled deviance is 1 but the
pearson deviance is 212 - I assume that this is not acceptable?

Thanks

Claire

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