I wrote a similar post just before, but I realized that I put wrong information there, hence I deleted it, and have re-written here
I am trying to conduct a power analysis on a hierarchical regression with interaction effects. Since my main hypothesis revolves around interaction terms, I am using ANCOVA in G*Power analysis to calculate the required sample size.
I have two categorical IVs (2 x 2), one continuous IV (I put this as a covariate in G*Power), and one continuous DV. I expect one two-way and one three-way interaction between the IVs. However, as far as I understand ANCOVA assumes no interaction between co-variates and IVs, whereas, in my case, there will be interactions.
In the above case, what should my numerator df be? I first thought it was 1, because (2-1)(2-1) = 1, but if I want to include the three-way interaction term between the categorical IVs and the continuous IV (covariate in G*Power), then should I add one more df in the power analysis? I have attached the screenshot of it below.