I am currently designing an experiment that I want to analyze using an RM ANOVA. Since some of the factors are confounded I need to do multiple ANOVAS. One analysis will be for 2x2 factors (within subject), the other will be for 4x2 factors (within subject). The second factor will be the same for both analysis, the first factor is only to control for possible item effects. I have some literature, from which I can estimate the efffect size for the second factor (the effect size was calculated using a regression there), I have no indication to estimate the first factor (I would still expect it to be close to zero for the 4x2 analysis and to find some effect for the 2x2 analysis).
I tried to look up within the G*Power manual if there is any way to estimate the sample size that would be needed. However, the manual is somewhat unclear about RM ANOVAS.
Is there any way to estimate the effect size for this kind of experiment?