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


From   Tinna <statalist@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Graphing ploynomial relationships after a regression
Date   Tue, 18 Oct 2005 14:02:23 -0400

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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