Re: One-Way Anova Repeated Measures: Main effect is significant, but post-hoc tests are not significant
Posted by
Ryan on
Jan 03, 2014; 5:43am
URL: http://spssx-discussion.165.s1.nabble.com/One-Way-Anova-Repeated-Measures-Main-effect-is-significant-but-post-hoc-tests-are-not-significant-tp5723746p5723757.html
JohnDoe,
Under certain conditions, it's perfectly acceptable to employ the Tukey HSD procedure as a follow-up procedure in testing all-possible pairwise comparisons in a repeated measures ANOVA. While it might take a little bit of effort, this procedure can be employed in SPSS for your design.
But let's step back for a moment. What is your understanding of the assumption of sphericity? How could a departure in sphericity affect the the sampling distribution of the ratio of mean squares? Are you familiar with the index, espilon? What is your estimate of epsilon? What is your understanding of the rule(s) of thumb regarding epsilon? What are the corrections offered by SPSS?
I really appreciated Bruce's question/comment about the "...nature of the repeated measures factor." It could have an impact not only on the post-hoc tests performed but the model as well (e.g., general linear model versus linear mixed model). For example, if your repeated measures variable is a measure of time, it's possible to observe a decay in correlations between residuals from observations more distant in time. This type of residual correlation structure could be modeled in the MIXED procedure. Sorry, but I can't resist plugging the MIXED procedure. :-)
Ryan