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Re: st: RE: RE: estimation with a time trend.

From   Maarten buis <>
Subject   Re: st: RE: RE: estimation with a time trend.
Date   Mon, 5 Jul 2010 05:14:56 -0700 (PDT)

--- On Mon, 5/7/10, natasha agarwal wrote:
> I am afraid I did not understand "year- (or -year-
> MINUS> midpoint) for interpretability?"

Say you have a variable representing year of birth
ranging between 1910 and 1980. I would then usually
have a line like this in my do-file:

gen c_year = year - 1910

Afterwards I would use c_year instead of year. In
this case "midpoint" is 1910, and makes sure that
your new variable is shifted to the left such that
it has the value zero in 1910. This makes sure 
that the baseline in your models refer to a point 
at the beginning of your observed period. This is 
particularly important if you include interactions 
or if you care about the constant (e.g. in a random 
effects model)

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen


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