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RE: st: Graphing Quadratic Interactions


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Graphing Quadratic Interactions
Date   Tue, 16 Dec 2008 12:42:00 -0000

In addition to Ronan's very thoughtful remarks: 

I think there were other reasons why Susanna got no replies before this
one. 

It wasn't very clear what she wants.  My guess was that she wants a plot
of predicted response in terms of X4 and X5, adjusting for X1 ... X3. As
mentioned on this list very frequently, Stata isn't serious at 3-D
graphics that might meet this need, whether contour plots or perspective
views. 

Just browsing the archives would have signalled the difficulty above. 

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

Ronan Conroy

This request has generated no replies as yet, and it's not hard to see  
why. Note, especially "I need a pretty graph"

I looked up "pretty graph" in Stata and there's no routine available,  
so we'll have to think this one out. Apologies - this is a long post.

[much detailed advice] 

Susanna Khavul

> I would like to graph a quadratic interaction after running rreg
> (Robust Regression). The model is as follows:
>
> xi:rreg Y i.X1 X2 X3 X4 X5 X5squared X5*X4 X5squared*X4
> (interaction terms are centered)
>
> Where:
> X5 -- independent variable
> X5squared--square of the independent variable
> X4-moderator
> X5*X4--independent variable x moderator
> X5squared*X4--independent variable squared x moderator
>
> The rest (X1 X2 X3) are controls which I want to account for as well.
>
> One standard deviation above and below the mean would be fine.
>
> I want to include both components of the interaction (linear and
> quadratic). Is there a module that will do it?  If not, what is the
> optimum graphing command.
>
> Any help would be much appreciated. I need a pretty graph.


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