Hello Christian,

There are several ways to elicit the results of a regression for a specific subset of your data.

1. Select the cases you want evaluated, then run the analysis. In SPSS, from the main menu bar, choose data/select cases.../ Then click the radio button for "If condition is satisfied" and click If... Then specify the desired subset by naming the appropriate selection variable(s) and the subset. For example: gender = 'F', or age > 35. Click Continue, then click OK. Proceed with desired analysis.

2. Within the regression subprogram, the dialog box contains an option to run the analysis on a specific subset. Enter the name of the variable in the box labeled "Selection Variable:", then click Rule button to specify the desired group/s. Proceed with the regression.

Good luck with your work.

To determine whether a third variable affects the relationship between two other variables, you need to test for interaction effects. In particular, it sounds like what you are calling Variable 3 is a categorical variable; if so, then you will need to do dummy variable regression. A good introduction to that topic (including interaction effects) is the Sage little green book by Hardy, Regression with Dummy Variables.

Thank you so much. I am doing it tonight to see if this gives me the data I was looking for.