Date:         Mon, 6 Jul 2009 14:23:17 -0400
Reply-To:     Doc Muhlbaier <lawrence.muhlbaier@DUKE.EDU>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Doc Muhlbaier <lawrence.muhlbaier@DUKE.EDU>
Organization: Duke University, Durham, NC, USA
Subject:      Re: Zero-inflated Poisson Regression
Comments: To: sas-l@uga.edu

One note if you are using SAS 9.2.  There is a bug in the output for ZIP
models in GENMOD:
http://support.sas.com/kb/36/040.html

Doc Muhlbaier
Duke
"Wensui Liu" <liuwensui@GMAIL.COM> wrote in message
news:1115a2b00907041019s5cdc36f4q6cb4c1d563621b55@mail.gmail.com...
> take a look at my sugi paper in 2008 "count data models in sas" and
> you should be able to find the answer.
>
> On Sat, Jul 4, 2009 at 3:01 AM, Newstat<chunyuanfei@gmail.com> wrote:
>> I am using zero-inflated poisson regression to do data analysis. The
>> outcome is number of hospitalization. 70% have never been
>> hospitalized, 18% were hospitalized once, and 5% twice. The follow-up
>> period (age) varied among the subjects. I have several questions.
>>
>> 1. the estimates in the Poisson part were not robust even when I
>> slightly changed the categories of some covariants, for example, two
>> age groups (<25 and 25-29 years old) were combined.
>>
>> 2. When I compared with the point estimates from overdispersed, they
>> were even in the opposite direction.
>>
>> I am quite confused about which model I shall choose. Could you please
>> help me figure it out? Your response is highly appreciated.
>>
>> Vivian
>>
>
>
>
> --
> ==============================
> WenSui Liu
> Blog   : statcompute.spaces.live.com
> Tough Times Never Last. But Tough People Do.  - Robert Schuller
> ==============================