Following the design and data described in this question, I did a simple one-way within-subjects repeated-measures (RM) ANOVA and found some significant p-values. I then applied non-orthogonal post-hoc Tukey's HSD tests, and when I got significant results I applied Holm-Bonferroni (1979) correction. Whenever some p-values survived the FWER correction, I calculated 95% CIs and mean for the associated pairwise comparisons.
My question is: If I don't observe a significant result at any of the above steps, do I have to carry out a power analysis for the RM ANOVA, apply Tukey's HSD test or Holm-Bonferroni adjustments, or do I simply report results from the RM ANOVA without doing the power analysis?
The problem is that I'm starting to immerse in biostatistics only after my experiments, and unfortunately I didn't run a power analysis beforehand.
Best Answer
The hardline view on post-hoc power calculation is: don't do it as it's pointless. Russ Lenth from the University of Iowa has an article on this topic here (He also has an amusingly facetious Java applet for post-hoc power on his website).