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RE: st: Graphing Quadratic Interactions

From   "Nick Cox" <>
To   <>
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

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

Just browsing the archives would have signalled the difficulty above. 


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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