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st: high correlation interaction & main effect


From   Caroline Wilson <wilson_cj@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: high correlation interaction & main effect
Date   Tue, 5 Mar 2013 05:12:29 +0000

Hi everyone,
I'm using Stata to run a multilevel model. I have a few interaction variables in my model, which are the product of a continuous variable (time) and a categorical variable. My variable for time was defined as years from the start of the study, to the nearest day, and was defined this way because it makes sense in the context of my study. The interaction variables are in some cases highly correlated (0.8) with the main effects.
A couple of questions:
1. How much should I worry about the high correlation?
2. What, practically speaking, can I do about the high correlation? I'd like to keep the interaction terms in the model since they represent my key research question.

Many thanks for any assistance!
Carrie 		 	   		  
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