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Re: st: Constraining OLS coefficients so that prediction satisfies a particular condition


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Constraining OLS coefficients so that prediction satisfies a particular condition
Date   Fri, 20 May 2011 15:44:37 +0200

On Fri, May 20, 2011 at 2:21 PM, Amer Hasan <amerhasan1@gmail.com> wrote:
> I would like to perform the following calculation using Stata 10.1SE
> on a windows xp machine.
>
> reg y1 x1 x2 if year==1
>
> predict y2-hat if year==2, xb
>
> such that y1 - y2-hat = K
>
> y1 - is observed
>
> y2-hat - is the prediction using betas of year 1 and Xs of year 2.
>
> K is the observed difference between y1 and y2 (also observable).
>
> I know I can constrain the betas and that should change the
> prediction. What I am not sure about is how to do so in such a way
> that the prediction satisfies the condition. Any guidance on how to
> start would be much appreciated. I may also not be seeing the forest
> for the trees.

I don't think you can do this with -constraints-, so you'll probably
have to write your own -ml- problem for this (if you were using Stata
11 I would say that -gmm- would fit nicer with the way you talk about
this problem.)

Hope this helps,
Maarten

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


http://www.maartenbuis.nl
--------------------------
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