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Re: st: poisson regression with lexis expansion and poisgof command

From   [email protected]
To   [email protected]
Subject   Re: st: poisson regression with lexis expansion and poisgof command
Date   Sat, 26 Mar 2005 12:46:17 EST

I am curious where you read that  GOF tests on Poisson data are best if done 
on compressed data - if this is what  you are saying.  There are certain GOF 
tests that require binomial (e.g.,  logistic regression) data to be compressed 
or grouped, but I have never seen a  reference to compression being better for 
count data. Since many count response  models use an offset, this amounts to 
nearly the same thing as grouping.   Regardless though, I see no reason for 
it. Do you recall the source?  

Joe  Hilbe

Dear  All,

I am a novice learing stata......this is probably very basic but Im  
struggling  a bit.
I have a cohort study of miners developing TB who  are HIV +ve or -ve 
over a 8 year study period..  I have found the best  poisson regression 
model testing with LRTs I have included a lexis expansion  for age of 
subject effects. The Stat manual  on poisgof  makes no  mention of 
compressing the data.  I have read that ungrouped data is  not correct 
for this command.

my final model looks like this   
xi:poisson _d ageband2 i.prevtb  i.sil if sil~=.,e(y)  irr

I have used the following commands to compress the data before doing  the 


. collapse (sum) _d y,by(hiv ageband2  job1 prevtb sil)

. xi:poisson _d ageband2  i.job1  i.prevtb  i.sil if sil~=.,e(y) irr
(output ommitted)

then   poisgof

I am sorry if there is insufficient information I am not sure how  much 
to  include.

Many thanks for help in this  matter.


Mark Tracy
Director and  Neonatologist
Nepean Newborn Intensive Care Unit
Lecturer  Department of Paediatrics and Childhealth
Sydney  University

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