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# RE: st: Negative binomial regression (nbreg): Plot an interaction effect of two continuous/interval variables

 From Cameron McIntosh To STATA LIST Subject RE: st: Negative binomial regression (nbreg): Plot an interaction effect of two continuous/interval variables Date Sat, 10 Sep 2011 12:06:27 -0400

```Fred,

I don't know if -1SD and +1SD are always the best values to use. I would recommend also trying a range of more "interesting/meaningful" values of your moderator to generate predicted probabilities for plotting. You should also take a look at these papers:

Buis, M.L. (2010). Stata tip 87: Interpretation of interactions in non-linear models. The Stata Journal, 10(2), 305-308.

Norton, E.C., Wang, H., & Ai, C. (2004). Computing interaction effects and standard errors in logit and probit models. The Stata Joumal, 4(2), 154-167.http://www.unc.edu/~enorton/NortonWangAi.pdf

Ai, C., & Norton, E. C. (2003). Interaction terms in logit and probit models. Economic Letters, 80, 123-129.

Hayes, A.F., & Matthes, J. (2009). Computational procedures for probing interactions in OLS and logistic regression: SPSS and SAS implementations. Behavior Research Methods, 41, 924-936. http://www.personal.psu.edu/jxb14/M554/articles/Hayes&Matthes2009.pdf

Francoeur, R.B. (2011). Interpreting interactions of ordinal or continuous variables in moderated regression using the zero slope comparison: tutorial, new extensions, and cancer symptom applications.International Journal of Society Systems Science, 3(1/2), 137-158.

Cam

> Date: Sat, 10 Sep 2011 17:35:53 +0200
> Subject: st: Negative binomial regression (nbreg): Plot an interaction effect of two continuous/interval variables
> To: statalist@hsphsun2.harvard.edu
>
> Dear users of statalist,
>
> I have a nbreg model containing 3 continuous variables and one interaction
> effect of two of these variables.
>
> How can I get a judicious plot of the interaction effect? A common method
> for plotting interactions effets in general is a graph, where one uses
> predications for -SD Mean +SD of both variables.
>
> How can I do that or another valuable plot in stata for nbreg? Or how can I
> use prvalue to calculate the needed values to put these data somehow in
> excel?
>
> Your kind help is highly appreciated.
>
> Fred
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```