re:st: Interaction and constraint

[Christopher Baum <kit.baum@bc.edu>]

<>
Now I want to simply the model by constrainning the second
(2.group#c.age) and the third terms (3.group#c.age) to be equal
(suppose that will improve the model fit), how should I do this?


With complete generality (which you can apply to other estimators, whether or not they allow constraint options),

use http://www.stata-press.com/data/r11/fvex, clear
g group23 = group==2 | group==3
regress y i.group i.group#c.age
regress y i.group group23#c.age

Kit



Kit Baum   |   Boston College Economics & DIW Berlin   |   http://ideas.repec.org/e/pba1.html
                              An Introduction to Stata Programming  |   http://www.stata-press.com/books/isp.html
   An Introduction to Modern Econometrics Using Stata  |   http://www.stata-press.com/books/imeus.html


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