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Re: st: Nested zip
From
Richard Williams <[email protected]>
To
[email protected], [email protected]
Subject
Re: st: Nested zip
Date
Tue, 06 Dec 2011 13:56:17 -0500
At 12:13 PM 12/6/2011, Kris Anderson wrote:
Hi,
I am trying to model a count variable (lifetime use of drugs) nested
in schools. Given it's distribution, a zip model would be ideal
(lots of zeros). However, it seems Stata will run an xtmepoisson but
not zip. Does anyone know why?
Best,
Kris
In Paul Allison's book "Fixed Effects Regression Models" he says (p.
68) that he does not consider zero-inflated Poisson and negative
binomial models because (1) they are more complex (2) there is little
software available for panel data (3) the negative binomial model
itself often provides a satisfactory fit to data with large numbers
of zero counts.
As a sidelight, he also argues (pp. 62-64) that the method used by
-xtnbreg- is not a true fixed effects method and gives examples of
where he claims xtnbreg gives nonsensical results. He offers some
alternative (albeit time-consuming) approaches. I'd be curious to
hear if StataCorp agrees or disagrees with Allison's critique. The
book is from 2009 but repeats an argument he made in a 2002 article.
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
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