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Re: st: ST: postestimation test

From   Maarten buis <>
Subject   Re: st: ST: postestimation test
Date   Fri, 6 Aug 2010 15:17:11 +0000 (GMT)

--- On Fri, 6/8/10, Bontempo, Daniel E wrote:
> The model showed the interaction of two factors was
> significant, and I thought I could use "test" to probe
> which pairs of means were actually different. But some
> comparisons involving the reference condition do not
> work, and I am not sure why the test is giving chisq.
> -----
> . margins condition#ageGrp
> . test 0.condition#1.ageGrp=1.condition#1.ageGrp

this test refers to the parameters in your model, not
to the table you get from margins. To test the differences
in predicted outcomes, you must first specify the -post- 
option in -margins-. 

-test- gives you a Chi square statistic  because it
produces a Wald test of possibly multiple constraints, in
which case it cannot use the normal distribution as the 
sampling distribution of the test statistic.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen


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