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This seems like a relatively very simple question compared to the apparent complexity on this forum.

I'm putting my PhD method together, within-subjects experimental design (counter-balanced related subjects experiment). My G-Power skills are limited, I want to know if there is more power using a matched-pair design or using blocks of participants. I initially considered comparing the group to a non-clinical group but using G-Power the sample size needed shot up beyond what I have access to.

It is a 2x2x3 design, 2 main factors, one with 2 levels, one with 3 levels. For understanding: I want to compare people wearing a pink t-shirt versus wearing a blue t-shirt on three different memory tests. The method of measurement is a MCQ test.

I can do this individually, as in one individual undergoes all conditions; or I can do it in groups, where blocks of participants undergo all conditions.

The available sample is 20-30 people. By my calculations I can get an effect size of 0.35 on Repeated Measures ANOVA tests using each person as their own control, in a sample size of 20.

I don't know how to calculate if using groups - possibly the same however interpreted differently in the context of being in a group?

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