I have made an experiment with 28 subjects. All made the experiments under 3 different conditions (A, B and C). So I have a table like this:

No. A B C
1   3 6 4
2   6 2 6

Now I just want to perform a RM-ANOVA or a Friedman test or a Quade test. That's not the problem.

I want to use GPower to determine the necessary alpha value to detect e. g. a "medium" effect. I do not get how to use GPower in this case.

Here is a screenshot of how I do it for a t-test:

enter image description here

Now I want to do the same for more than 2 conditions. Can somebody point out how to do that? Here's a screenshot of the possibilities:

enter image description here

EDIT: I looked it up, and apparently it is called One-way repeated measures ANOVA. So how can I to One-way repeated measures ANOVA with G*Power to determine the required alpha value (given effect size and so on)?


1 Answer 1


I think I found it here:

Link to book chapter, additional material

Applied to my problem I guess it will be like this:

enter image description here

F tests - ANOVA: Repeated measures, within factors
Analysis:   Criterion: Compute required α 
Input:  Effect size f   =   0.25
    Power (1-β err prob)    =   0.80
    Total sample size   =   28
    Number of groups    =   1
    Number of measurements  =   3
    Corr among rep measures =   0.3
    Nonsphericity correction ε  =   1
Output: Noncentrality parameter λ   =   7.5000000
    Critical F  =   2.2129741
    Numerator df    =   2.0000000
    Denominator df  =   54.0000000
    α err prob  =   0.1191999

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