Hi all,
I'm hoping someone may be able to help me with this. If not, doesn't matter really, but I can't figure out the answer and it's doing my nut in!
So, a typical experiment design in my PhD is a 2 by 2 repeated measures design where BOTH variables are repeated measures. So, I've got 2 IVs, both with 2 levels, both repeated measures. Sometimes I have a mixed design - 2 by 2 by 2 with 2 repeated measures IVs and 1 between participants factor.
Does anyone know how I can calculate the power in this design? I get statistically significant interactions (with pretty strong effect sizes according to partial eta squared) but the simple main effects are non-significant. So, that indicates a lack of power. I would like to know how much power it lacks, and how many participants would be needed to prevent the type 2 error that I appear to be experiencing. (Not that I'm going to go out and run more participants, but I think the argument I'm presenting would be stronger if I had the numbers).
I've been using G*Power (hello high learning curve!) and I've figured out how to do a power analysis for a one-way repeated measures ANOVA, as well as a power analysis for a Mixed ANOVA (as long as it's 1 within and 1 between factor). But, I can't figure out how to enter the data so I get the correct degrees of freedom and accommodate the correlations between my multiple repeated measures variables.
Does anyone know how to do this? Either using G*Power or with some other (Mac) software or online resource?
THANKS in advance,
Anna
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