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Re: st: ST: postestimation test


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
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
<snip>
> . 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

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

http://www.maartenbuis.nl
--------------------------


      

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