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RE: st: RE: Graphing ploynomial relationships after a regression


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Graphing ploynomial relationships after a regression
Date   Tue, 18 Oct 2005 19:13:16 +0100

That's good. Do join in. 

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

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Tinna
> Sent: 18 October 2005 19:02
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: RE: Graphing ploynomial relationships after a
> regression
> 
> 
> Hello Maarten and Nick,
> 
> I do not mean to stop your discussion, which I am learning a bunch
> from, but I wanted to thank you and tell you that I have my desired
> graph now.
> 
> Tinna
> 
> On  10/18/05, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> > As a model gets more complex, it is less likely that it can
> > be presented by a graph. y = polynomial(x) is one exception, but
> > in practice even cubics over a whole range are unlikely to be
> > useful, in my experience.
> >
> > But, more to the point, a model gets more complex, you have _more_
> > to type as you spell out each term as _b[varname] * 
> varname. -predict-
> > does this all for you. And this is error-prone.
> >
> > Other than the occasional pedagogic advantage of underlining
> > what is being done, i.e. plugging estimates into a model
> > formula, I can't understand your preference here.
> >
> > Nick
> > n.j.cox@durham.ac.uk
> >
> > Maarten Buis
> >
> > > True, though I find it easier to continue to use my approach
> > > when my model gets more complex.
> > >
> > > n j cox wrote:
> > >
> > > > Even with Maarten's example, things can be made
> > > > simpler. Starting as before,
> > > >
> > > > sysuse auto, clear
> > > > gen weight2 = weight^2
> > > > reg price weight weight2
> > > >
> > > > if you
> > > >
> > > > predict quad
> > > > twoway mspline quad weight || scatter price weight
> > > >
> > > > you get the data shown as well.
> > > >
> > > > Alternatively, if you install the -modeldiag- package
> > > > from either SSC or the Stata website, then
> > > >
> > > > predict quad
> > > > regplot
> > > >
> > > > will give you the same graph. This is because -regplot-
> > > > defaults to a plot of the observed and predicted response
> > > > against the first predictor named.
> > > >
> > > > Maarten Buis
> > > >
> > > > sysuse auto, clear
> > > > gen weight2 = weight^2
> > > > reg price weight weight2
> > > > sum weight
> > > > twoway function y = _b[_cons]+_b[weight]*x+_b[weight2]*x^2,
> > > range(1760
> > > > 4840)
> > > >
> > > >
> > > > Tinna
> > > >
> > > > I am using an independent variable in its regular and
> > > squared forms in
> > > > an OLS and 2SLS regressions.  Can I graph this polynomial
> > > relationship
> > > > as indicated by the regression in an easy way?

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