RE: st: interaction without linear terms ( I am sorry)

["Mentzakis, Emmanouil" <e.mentzakis@abdn.ac.uk>]

I am really sorry. That was a private communication that accidentaly got
posted to statalist. 

Appoogies again 
Manos

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Mentzakis,
Emmanouil
Sent: 23 May 2007 16:32
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: interaction without linear terms

I didn't really understand what exactly I should lokk at. However,
regarding the standard errors, my problem is not obtainign the std
errors but obtaining the variance. I know how to compute the errors for
an already given the variance. 


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Mirko
Sent: 23 May 2007 14:39
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: interaction without linear terms

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".

Hope this helps
Mirko

On 5/23/07, Richard J Stoll <stoll@rice.edu> wrote:
> 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.
>
>
> ----------------------------------------------------------------------
> -- Richard J. Stoll * Professor of Political Science * Rice University

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