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Re: st: results of interaction term


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu
Subject   Re: st: results of interaction term
Date   Thu, 17 Mar 2005 15:58:32 -0500

At 03:43 PM 3/17/2005 -0500, Jian Liu wrote:
Dear list members,

I've a question regarding interpretation of the results of interaction term from multiple regression model.
before introducing interaction term, the results from MR were:
x1 (continuous) significant
x2 (binomial) significant
after introducing the interaction term x1x2, the results from MR were:
x1 significant with no change of coefficient
x2 not significant with a change of coefficient
x1x2 not significant

So how do we interpret the results as such? thanks for your help.
The interpretation of main effects gets trickier once you start including interaction terms; in particular, you probably shouldn't get too concerned about x2 becoming insignificant because it has a different meaning once you add the interaction term. Centering vars can help make interpretation easier. This is discussed a bit at

http://www.nd.edu/~rwilliam/xsoc593/lectures/l52.pdf

Based on what you are saying, it sounds like you want to leave the interaction term out.


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Richard Williams, Notre Dame Dept of Sociology
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