Talk:Interaction between categorical and continuous variables

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Centering the categorical variable in this case would also be necessary, unless you want the regression to return coefficients that apply to the population of people with a score of 0 on the categorical variable (and since I'm assuming one would code the example categorical variable 1,2, this would be meaningless). See this reference for a good discussion: Kraemer, H. C., & Blasey, C. M. (2004). Centring in regression analyses: a strategy to prevent errors in statistical inference. International Journal of Methods in Psychiatric Research, 13(3), 141-151. doi:10.1002/mpr.170

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