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st: RE: -prgen- with a quadratic function


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: -prgen- with a quadratic function
Date   Tue, 15 Mar 2005 22:03:34 -0000

I don't think Scott Long is a member of Statalist. 

No matter: your problem should yield to -adjust- 
followed by an appropriate graph. 

Nick 
n.j.cox@durham.ac.uk 

Mariano Sana
 
> Hi Statalisters.  Someone experienced with ?prgen- might be 
> able to answer this.
> 
> I ran a logit model that has, among its predictor variables, 
> AGE and AGESQ.
> The coefficient for AGE is positive and the coefficient for AGESQ is
> negative.  The turning point is at age 79 or so.  I?ve been trying to
> generate a graph that shows how predicted probabilities vary 
> by age for a few groups in my analysis.  I used the ?prgen- command from 
> the Spostado package.
> 
> The graph that I get doesn?t make sense. The probability 
> increases nonstop
> and becomes asymptotic to 1 at age 90 or so.
> 
> I realize that the problem is that ?prgen- cannot vary the 
> value of AGESQ
> as the value of AGE varies.  The default for AGESQ is the 
> mean of AGESQ,
> unless I specify another value.  Obviously, I need AGESQ to 
> be the square of AGE as AGE varies.
> 
> By now I think I have no other solution than running 
> ?prvalue- (also from
> the Spostado package) multiple times to get the probabilities 
> I need for
> the graph. Or is there any other way? Is this a question for 
> Scott Long?

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