Power analysis for RM-ANOVA I have tried running power analyses for both a 2x2 and 2x3 repeated measures-ANOVA (same alpha, power, etc). The results suggest I need more participants for the 2x2 design than the 2x3 design and i am struggling to conceptualize why? Is this the case, or am I likely calculating something wrong? If it is correct can someone please explain why?

This depends on your null hypothesis and the nature of your question.
But think of it as the quantity of information. If you have a 2x3 and a 2x2 with the same number of participants, you have more information in the 2x3. If you have more information, you have more power.
