I have a set of models that are the result of a multiple linear regression. I would like to calculate the power for each of these models. I found this tutorial on calculating the power using G*Power. Since the data has already been collected, I am using the Post Hoc type of Power Analysis, and I was hoping to use the "Determine" button to automatically calculate the effect size. However, I see that one need to provide a partial R2, but I would think that for a multiple linear regression (which I think would have multiple partial R2 values), it would make more sense to provide the R2 for the resulting model. Am I misunderstanding the difference between R2 and partial R2? If so, how do I obtain the partial R2 to use in G*Power?
In GPower, you do a power for an R2 in multiple regression by doing the partial R2 with no predictors in the baseline model.
To do this, set the total number of predictors to 1, and the number of tested predictors to 1. You're then testing the model against an intercept only model, with an R2 of zero.
(You can always think of regression models in this way - you're testing against no predictors, and looking at the change in R2.)