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Re: st: How to get marginal effect of quadratic term in tobit model in stata 11.0


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to get marginal effect of quadratic term in tobit model in stata 11.0
Date   Mon, 18 Jul 2011 13:18:05 +0200

On Mon, Jul 18, 2011 at 1:07 PM, lutunnahar begum wrote:
> I am using stata 11.0. I am interested in non-linear effect of some of
> the regressors in tobit model....but for tobit, we don't get any
> marginal effect for quadratic term.

And that is exactly as it should be. Conceptually, adding a squared
term of a variable x only means that x has a non-linear effect. So
there is only one variable x. The fact that the the variable x is
entered in the model as two "variables", x and x^2, does not change
the fact that from a substantive point of view there is only one
variable. Maybe you find the following helpful:

<http://www.maartenbuis.nl/publications/inter_quadr.html>

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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