I have read on the StatSoft website that it is possible to test interactions with an ANCOVA (although it was considered as a case where the assumptions for this analysis are violated in some old statistical books).
I am trying to test the interaction between a between-subject variable Group and a within-subject variable Treatement, while covariating for IQ.
When running this analysis on Statistica, I get the main effect of Group, the main effect of Treatment, but no interaction between Group and Treatment.
Do you know how to display the result of this interaction?
Thank you very much,
Instead of using the ACOVA module, go to General Linear Model. Specify Score as your DV, Group as you categorical predictor and IQ as your continuous predictor. Modify your between group design so that it is full factorial (or customize it however you want it) and proceed from there. GLM gives you the greatest flexibilty.