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Re: st: centred mean age

From   David Hoaglin <>
Subject   Re: st: centred mean age
Date   Wed, 30 Jan 2013 20:30:02 -0500

Nick's suggestion (below) is an important one.  If the relation of
your dependent variable to age is nonlinear, the first step should be
to investigate the nature of the nonlinearity.  If you have done that,
and concluded that a single cubic polynomial is a reasonable
description, OK.  Often, mechanically adding a quadratic term (and a
cubic term) to the model is not appropriate.  Many people do that, and
produce poor analyses as a result.

Related to Rich's comment, in a multiple regression (or similar)
model, the definition of each regression coefficient includes the list
of all the other predictors.

David Hoaglin

On Wed, Jan 30, 2013 at 3:20 PM, Nick Cox <> wrote:
> All that said, there are quite possibly better ways of doing what you
> want, such as cubic splines or fractional polynomials, which are well
> supported in Stata.
> Nick
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