Repeated measures ANOVA contrasts

Question

I'm running a repeated measures ANOVA with a 3-level DV. Now what I've read is that you only look at the post-hoc test if the within-subject (overall) effect is significant. What about the within-subject contrast: what if the effect is not significant, but certain levels in the contrasts are?

Two (related) questions: 1) would you report the significant contrasts despite the not significant effect? Or is it just as with post-hoc that you would ignore the contrasts completely if the effect is already not significant. 2) can you look at the post-hoc test if certain contrasts are significant?

Answer 1

Recall, in repeated measures ANOVA, there is a within-group effect $(W)$, a between group-effect $(B)$, and the interaction $(B*W)$. The within-group effect reveals how the response values change over time within each group. If responses never change within a particular group and are constant, then $W$ won't be significant. For the between-group effect $B$, this basically compares ovarall mean response differences between groups. The real focus is the $B*W$ interaction, since it lets you know if the groups differ in their reponse over time, such as linear, quadratic, or U-shaped dose-response curves. For contrasts, they are by definition, all post hoc, so you can do whatever you want. Yes, you can report significant all-possible mean comparisons between groups and times whatever fashion you want -- just make sure you state that e.g. "during post-hoc analyses, we identified significantly different means between sub-groups x,y,z and/or times 1,2,3." The key is to preface your statement with "post-hoc," after which you can literally perform any tests you desire.