AND or OR, that’s the question [Power / Sample Size]

posted by Helmut Homepage – Vienna, Austria, 2022-08-11 17:25 (114 d 20:44 ago) – Posting: # 23216
Views: 3,013

Hi Chris,

❝ After some thoughts, I am wondering if the sample size estimation only considers one comparison. I found an old following post regarding this topic.


Oh dear, that one! Opening Pandora’s box. However, only relevant if one would assess the study with the ‘All at Once’ approach (i.e., an ANOVA of pooled data). The jury left the courtroom 2½ years ago and hasn’t returned ever since…

❝ If we are considering both T1=R and T2=R, perhaps, we need to look at the bivariate distribution of the two test statistics when looking at the power. And these should be correlated as well, which makes things complicated. I am maybe missing something and was wondering if you could enlighten me on this subject.


In the ‘Two at a Time’ approach T1 and T2 are treated independently. Hence, you have two separate distributions. You see that also in the evaluation, where you obtain two residual variance estimates.

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