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Re: st: main effect insignificant, interaction term significant

From   Richard Goldstein <>
Subject   Re: st: main effect insignificant, interaction term significant
Date   Wed, 16 Feb 2011 11:16:50 -0500

it looks like these are each binary (dichotomous) variables; you will
find it much easier to deal with if you make one of the 4 possibilities
the reference group (e.g., male-neversmoked) and form dummies for each
of the other 3 (male-smoke, female-neversmoked, female-smoked)

re: your specific question, you should look at Nelder, JA (1998), "The
selection of terms in response-surface models -- how strong is the
weak-heredity principle?", _The American Statistician_, 52: 315-318


On 2/16/11 11:13 AM, Gáti Annamária wrote:
> Dear All,
> I know that there is a never ending debate on this, but I am interested
> in your opinion.
> Do (and if so, how do) we interpret interaction terms in the following
> regression example:
> we want to explain whether someone got lung cancer or not and we explain
> this by gender and smoking.
> gender= non sign.
> ever smoked= non sign.
> gender*smoked= sign
> annamaria
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