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# st: Problem probing interaction

 From Kris Anderson To statalist@hsphsun2.harvard.edu Subject st: Problem probing interaction Date Tue, 11 Jan 2011 13:20:26 -0800

```Hi, all.

```
I am trying to plot a 2-way continuous vs continuous interaction in logistic regression using multiple imputation. I have successfully done this for 3-way interactions using different code. I found this code on the site but can't get it to run.
```
```
mim: logistic drinker gradeR sexR his_latR white C_ndmot C_socmot C_copemot C_enhmot C_confmot int_nsoc int_ncope int_nenh int_nconf gen y1 = _b[C_socmot]*(-1.18) + _b[C_ndmot]*C_ndmot + _b[int_nsoc]*(-1.18)*C_ndmot + _b[_cons] gen y2 = _b[C_socmot]*(0) + _b[C_ndmot]*C_ndmot + _b[ int_nsoc]*(0)*C_ndmot + _b[_cons] gen y3 = _b[C_socmot]*(1.18) + _b[C_ndmot]*C_ndmot + _b[ int_nsoc]*(1.18)*C_ndmot + _b[_cons]
```sort C_socmot
```
twoway (line y1 ) (line y2 C_socmot) (line y3 C_socmot), name(SocmotxNdm, replace)
```gen p1 = exp(y1)/(1+exp(y1))
gen p2 = exp(y2)/(1+exp(y2))
gen p3 = exp(y3)/(1+exp(y3))
```
twoway (line p1 C_socmot) (line p2 C_socmot) (line p3 C_socmot), name(SocmotxNdm, replace)
```
```
I am getting an error message after the gen y1 line saying that "no variables defined." The code looks like my sample so am a bit confused.
```
Thanks,
Kris
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```