I need to carry out a hierarchical multiple regression. My data consists of one continuous dependent variable, 2 continuous predictor variables and a categorical IV with 3 levels.I need to assess whether an interaction effect occurs between each of the continuous predictor variables and the categorical IV in predicting my DV. I have read that it is necessary to dummy code k-1 variables with k being the number of levels in the categorical variable, is this correct in my case? If so then I would have 2 binary dummy variables.
To create the interaction term do I then multiply my predictor variable x dummyvariable1 x dummyvariable2 and enter this term in the model? Or do I create 2 interaction terms: 1 created by multiplying my predictor x dummyvariable 1 and another by multiplying my predictor x dummyvariable2 and then enter both of these terms in the model simultaneously? I am an undergrad psychology student so I don't have a great knowledge of stats and have struggled to find an answer to this question in my reading that I can understand. I will be using SPSS. Any help would be really appreciated, even if you could direct me to some reading. Thanks!