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Re: st: Shapes of two Inverted U curves (same model on two different samples)


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Shapes of two Inverted U curves (same model on two different samples)
Date   Mon, 4 Jul 2011 21:28:58 +0200

On Mon, Jul 4, 2011 at 7:12 PM, L.M.A. Mulotte wrote:
> I have an OLS model that includes both a linear effect and the quadratic term. I run this model on two samples, one with a treatment (sample X) and one without treatment (Sample Y). <snip> Is there any means to test whether the "legs" of Curve Y are steeper than the "legs" of Curve X?

The curve with the largest absolute value of the parameter on the
squared term will have the steepest legs, i.e. will be more peaked. So
you can just use -test- to test the hypothesis that the parameters for
the squared term in the treatment sample and the control sample are
the same, which corresponds to the hypothesis that the two curves are
equally steep.

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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