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RE: st: interaction without linear terms


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: interaction without linear terms
Date   Wed, 23 May 2007 14:49:43 +0100

This wisdom is shared by others. See comments embedded
within 

McCullagh, P. and Nelder, J.A. 1989. Generalized linear
models. London: Chapman and Hall. 

on whether the origin is special. 

I add a small comment on the original formulation. 
This is essentially a statistical question, and not 
an econometric question. 

Nick 
n.j.cox@durham.ac.uk 

Mirko
 
> I really invite you to have a look at this web page by Matt Golder
> full of hints about multiplicative interaction terms, correct standard
> errors and Stata codes, which is a companion of:
> 
> Thomas Brambor, William Roberts Clark, Matt Golder
> "Understanding Interaction Models: Improving Empirical Analyses"
> (Political Analysis 14: 63-82),
> 
> http://homepages.nyu.edu/~mrg217/interaction.html
> 
> Regarding your point and in brief, they say:
> 
> "We recommend that scholars include all constitutive terms in their
> interaction model specifications".
 
Richard J Stoll 

> > On Wed, 23 May 2007, Wanli Zhao wrote:
> >
> > > I have a basic(?) econometric question on regressions 
> with interactions. My
> > > search on this did not product much. Do I have to include 
> the linear terms
> > > in the regression when I also have interactions (include 
> x & y when I have
> > > x*y)?  What does it mean when I drop x, or y or BOTH 
> (always keep x*y)? Any
> > > help is highly appreciated (occasions where different 
> model is suitable),
> > > especially what I should get to read!
> > >
> >
> > Yes.
> >
> > The "classic" article in political science is:
> > Friedrich, Robert. 1982. "In Defense of Multiplicative 
> Terms in Multiple
> > Regression Equations." American Journal of Political 
> Science 26: 797-833.

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