Stop estimating post hoc power! [Power / Sample Size]

posted by ElMaestro  – Belgium?, 2017-12-26 14:11  – Posting: # 18087
Views: 22,367

Hi kms.srinivas,


I know this post-hoc power business can be very tricky.

Try and ask yourself which question post-hoc power actually answers. Try and formulate it in a very specific sentence.

Generally, [given a statistical model] power is the chance of showing BE in a trial if your expectations about GMR, CV are correct when you use N subjects.
Choice of GMV, CV and N to plug in a power calculation is up to the user, but in the specific case of post-hoc power stats software may make such a choice for you without asking. Often it is 95% or 100% regardless of what you observed in the previous trial.

So with this in mind try and look back in your figures and tell which question the post-hoc calculation in your case gave an answer to. Feel free to paste your numbers here then I am sure someone can help working it out. You might get surprised.:-)

I could be wrong, but...
Best regards,
ElMaestro

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