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Re: st: Nested zip

From   Muhammad Anees <>
Subject   Re: st: Nested zip
Date   Wed, 7 Dec 2011 06:41:51 +0500

First use -findit zip- on your Stata command bar, and also -ssc
install zip, replace- installs it. Again if not possible (I am not
sure it would not be possible), also one possible choice for such
situations may be the -hurdle- type models like -ztpnm-. Same -findit-
applies and is available from -net sj 11-1 st0218-.
Hope this works.

On Tue, Dec 6, 2011 at 11:56 PM, Richard Williams
<> wrote:
> 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:  Richard.A.Williams.5@ND.Edu
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Muhammad Anees
Assistant Professor
COMSATS Institute of Information Technology
Attock 43600, Pakistan

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