Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: Poisson and NBREG


From   "Kieran McCaul" <kieran@dph.uwa.edu.au>
To   "Statalist" <statalist@hsphsun2.harvard.edu>
Subject   st: Poisson and NBREG
Date   Fri, 27 Sep 2002 14:08:18 +0800

In the two models below I'm using the same data.  The first run is a Poisson
analysis, the second a negative binomial (B1 in Cameron and Trivedi
parlance).

Now as far as I know my betas should bethe same in both models.  the only
thing that should change are SEs and p-values.

So why am I getting different betas.

What am I doing wrong here?


. poisson alfil1a group, expos(filter1)

Poisson regression                                Number of obs   =
34
                                                  LR chi2(1)      =
34.27
                                                  Prob > chi2     =
0.0000
Log likelihood = -341.07851                       Pseudo R2       =
0.0478

----------------------------------------------------------------------------
--
     alfil1a |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+--------------------------------------------------------------
--
    grouping |   .6831764   .1200077     5.69   0.000     .4479656
.9183873
       _cons |  -2.313518      .2073   -11.16
0.000    -2.719819   -1.907218
     filter1 | (exposure)
----------------------------------------------------------------------------
--

. nbreg alfil1a group, expos(filter1) disp(const)

Negative binomial (constant dispersion)           Number of obs   =
34
                                                  LR chi2(1)      =
0.73
                                                  Prob > chi2     =
0.3932
Log likelihood = -116.99016                       Pseudo R2       =
0.0031

----------------------------------------------------------------------------
--
     alfil1a |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+--------------------------------------------------------------
--
    grouping |   .2718017   .3178545     0.86   0.392    -.3511816
.8947851
       _cons |  -1.649793   .5384459    -3.06
0.002    -2.705127   -.5944583
     filter1 | (exposure)
-------------+--------------------------------------------------------------
--
    /lndelta |   2.506257   .3217237                       1.87569
3.136824
-------------+--------------------------------------------------------------
--
       delta |   12.25896   3.943999                      6.525323
23.03061
----------------------------------------------------------------------------
--
Likelihood ratio test of delta=0:  chibar2(01) =  448.18 Prob>=chibar2 =
0.000


_______________________________________________________________________
Kieran McCaul
School of Population Health
University of Western Australia
35 Stirling Hwy
Crawley, 6009
Australia
Phone:-61-8-9380-1274
Mobile: 0403-00-33-82
Fax:	-61-8-9380-1188
email:kmccaul@cyllene.uwa.edu.au
      kieran@dph.uwa.edu.au
web:	http://www.publichealth.uwa.edu.au/

______________________________________________________________________
IMPORTANT: This email is intended for the use of the individual
addressee(s) named above and may contain information that is
confidential, privileged or unsuitable for overly sensitive
persons with low self-esteem, no sense of humour or irrational
religious beliefs. If you are not the intended recipient, any
dissemination, distribution or copying of this email is not
authorised (either explicitly or implicitly) and constitutes an
irritating social faux pas.

CRICOS provider code (00126G)
______________________________________________________________________

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index