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Re: st: oglm and heterogeneous choice models


From   Richard Williams <richardwilliams.ndu@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: oglm and heterogeneous choice models
Date   Mon, 24 Oct 2011 19:01:54 -0500

At 05:44 PM 10/24/2011, Cameron McIntosh wrote:
Rourke,

I might add that if you're going to be looking at interactions in this type of model, you should see:

Mallick, D. (January 2009). Marginal and Interaction Effects in Ordered Response Models. MPRA Paper No. 13325.http://mpra.ub.uni-muenchen.de/13325/1/MPRA_paper_13325.pdf

I wasn't familiar with that article. Just skimming through it, I notice it is using Stata 10 and the old -mfx- command. Part of the problem with -mfx- is that it doesn't realize when variables are dependent on each other, e.g. it doesn't know that if x1x2 = x1*x2, then if x1 = 0 x1x2 must equal 0 as well. Factor variables and the margins command addressed those concerns in Stata 11.

I must confess, I get confused by all these discussions about the marginal effect of an interaction term. The margins command doesn't even report a separate marginal effect for the interaction term -- instead it just reports marginal effects for the terms used to compute the interaction. That makes sense to me, since an interaction term can't change without either or both of its component parts changing. So, I am not quite clear on what people want or expect when they ask for the marginal effect of an interaction term. Maybe I just need to break down and read these articles more carefully!


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Richard Williams, Notre Dame Dept of Sociology
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