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st: linear, quadratic terms and centering


From   Fabio Zona <fabio.zona@unibocconi.it>
To   statalist@hsphsun2.harvard.edu
Subject   st: linear, quadratic terms and centering
Date   Sat, 21 Aug 2010 09:40:06 +0200 (CEST)

Dear Statalist,

a very simple question: I have 

y = c + x0 + x1 + x1square

In order to center x1 and x1square, do I first need to calculate the square term and afterwards to center both the linear and the quadratic term around their respective means?
Or do I first center the linear term and calculate the square term on the basis of the "centered" linear term ?

I guess that the first alternative works.

Thanks

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