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st: Count Data again


From   Markus Köller <markus-koeller@web.de>
To   statalist@hsphsun2.harvard.edu
Subject   st: Count Data again
Date   Thu, 28 Feb 2008 18:37:03 +0100

Hello everyone,

thx again for the help about my last question. I read some stuff about Count Data models now and I have another question...

-> I am trying to predict the total number of children a woman gives birth to. I want to use a Count data model with a Poisson-regression.
-> I am using crosssectional data which has been collected within three waves. Total number of observation is 1350.

-> The mean of my variable "amount of children" is 1,27 and my variance of this variable is 1,131.

-> I see that my variable seems to be underdispersed, since the mean exceeds the variance.

My question is: The mean is bigger than the variance, but is it really "too" much, so that one can speak about "underdispersion"?  To me, 1,27 and 1,131 seems not so very different. And if it is not underdispersed, does it mean, that normal Poisson-distribution is the correct approach?

Have a nice evening and thanks everyone,
Markus.
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