Re: st: interaction graph

[fabio.zona@unibocconi.it]

Hi,

In a 2-D graph, isn't it possible to "fix" the value of the continuos moderator at some values (i.e. creating a dummy variable, for instance for values below the first quatile and above the third quartile) and use regplot?

I think I found interact long time ago on the internet, saying it was downlodable. I did not know it was not an official command.





----- Messaggio originale -----
Da: "Nick Cox" <njcoxstata@gmail.com>
A: statalist@hsphsun2.harvard.edu
Inviato: Mercoledì, 23 febbraio 2011 10:47:39 GMT +01:00 Amsterdam/Berlino/Berna/Roma/Stoccolma/Vienna
Oggetto: Re: st: interaction graph

I don't have a specific suggestion.

Your model produces a prediction surface and although there are some
user-written commands for 3-D graphics plotting the entire surface is
a problem for which you are better off outside Stata.

On the other hand, generating predictions for a few fixed values of
your moderator might produce an adequate graph.

-interact- is not an official command. It follows that you should
explain where it comes from, as long and often requested on this list.

Nick

On Wed, Feb 23, 2011 at 9:34 AM, Fabio Zona <fabio.zona@unibocconi.it> wrote:

> time ago you suggested to use
>
> regplot x, separate(dummy)
>
> to graph interaction effect between a continuous variable and a dummy variable.
>
>
> However, what command should I use if I have
> a) a quadratic form (i.e.,   x  +  x_square)
> b) the moderator is a continous variable (not a dummy), and it is multiplied by both x  and  x-square ??
>
> The stata command "interact" works only with linear (i.e. non quadratic) models

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