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When is is appropropriate to include or exclude the intercept from a regression model? SPSS provides this option in the GLM menu.
I am assessing group difference (gender) on tasks performed (X) and income earned (Y). In this case, if no task is performed, then no income is earned.
The SPSS guidelines states here:
"Include intercept in model. The intercept is usually included in the model. If you can assume that the data pass through the origin, you can exclude the intercept."
My stats knowledge is a bit rusty now but I remember my teacher saying that you should never exclude the intercept!