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st: interaction term in negative binomial regression


From   "Sheng Wang" <wang.589@osu.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: interaction term in negative binomial regression
Date   Mon, 11 Apr 2005 15:41:54 -0400

Dear all:

I have a question about how to interpret the interaction term in negative
binomial regression results.

Below is the section from the stata output, gender and usage are two control
variables. Dummy is a dummy variable created for 2 conditions (0 or 1).
Extraversion is considered a continuous variable (1-5), and interaction is a
product of the dummy variable and the mean-centered extraversion. I'd like
to understand the different relationships between extraversion and quantity
under condition =0 or condition =1? How can I calculate if there is a
stronger relationship between extraversion and quantity under the two
different conditions? 

 
    Quantity |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
Interval]
-------------+--------------------------------------------------------------
--
      gender |   1.215867   .3982474     3.05   0.002     .4353161
1.996417
       usage |   .2103553   .1310798     1.60   0.109    -.0465563
.467267
       dummy |   4.035392   .6155144     6.56   0.000     2.829006
5.241778
extraversion |   1.946443   1.131335     1.72   0.085    -.2709335
4.163819
 interaction |  -2.616264   1.203618    -2.17   0.030    -4.975313
-.2572159
       _cons |  -10.07717   4.202655    -2.40   0.016    -18.31423
-1.840122
-------------+--------------------------------------------------------------
--

 
I would really appreciate any assistance with this issue.

Sincerely,

Sheng Wang
The Ohio State University





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