I would like to perform an a priori power analysis to calculate required sample size for data to be analyzed using one way ANOVA and Tukey HSD post hoc test. (I want to determine pair-wise which groups are different from each other)

desired significance level (alpha): 0.05 desired power: 0.9 cohens effect size: 0.4 nr of groups: 3 or 5

I want to calculate sample size. I have used G*Power but it seems to only provide the power analysis for ANOVA omnibus test but not the post hoc test.

Alternatively, would it be valid (and conservative) to correct alpha a la Bonferroni by dividing 0.05 by the number of the unplanned multiple comparisons? (e.g. 0.05/3 for three groups or 0.05/10 for 5 groups) and use that lower alpha for G*Power's f-test power analysis?

Or should I count up all pair-wise comparisons and perform a power analysis for a t-test using this Bonferroni adjusted alpha?

Can anyone provide a reference or software or any other guidance on how to proceed?


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.