step  To run a GLM Univariate analysis, from the menus choose:

Analyze
  General Linear Model
   Univariate...

step  Click Reset to restore the default settings.

step  Select Income after the program as the dependent variable.

step  Select Program status as the fixed factor.

step  Select Income before the program as the covariate.

step  Click Model.

step  Select Custom as the model type.

step  Select prog(F) and incbef(C) in the Factors and Covariates list.

step  Select Main effects from the Build Term(s) drop-down list and select the main effects to the model.

step  Select prog(F) and incbef(C) in the Factors and Covariates list.

step  Select Interaction from the Build Term(s) drop-down list and select the interaction term to the model.

step  Click Continue.

step  Click Options in the GLM Univariate dialog box.

step  Select Estimates of effect size in the Display group.

step  Click Continue.

step  Click OK in the GLM Univariate dialog box.

These selections produce a model with an interaction between the factor prog(F) and the covariate incbef(C).