http://spssx-discussion.165.s1.nabble.com/Simple-Main-Effects-Pairwise-Comparisons-vs-Univariate-Tests-tp5726323p5726331.html
More detail would help, for seeing entirely what you have done, but the questions
at the end are not too tough.
In reverse order:
(Explaining...) Plot your means. Is there a simple description? If not, you might
economically "explain these findings" as Type II error.
(Univariate...) Univariate tests on 3 groups do not have to show 2-group effects
as "significant" when there were barely differences on 2 groups tested alone.
The extra power from having fewer d.f. being tested is one reason why designs
with two groups are inherently superior to designs with three groups.
(interaction) The interaction is tested using within-subject variation, which your
followup tests do not. Trends across time are easier to test and report when you
can use the linear trend component. If you do not expect "linear" as the nature
of your change, perhaps the design is wrong: you could use Baseline as a covariate,
or else test primarily Base versus Other. Or, if you do not expect change across
time, is there some other reason to be interested in random effects seen when
doing a lot of tests?
--
Rich Ulrich
> Date: Tue, 3 Jun 2014 16:29:27 -0700
> From:
[hidden email]> Subject: Simple Main Effects Pairwise Comparisons vs Univariate Tests
> To:
[hidden email]>
> I have an experimental design with Time as the within-subjects factor (3
> levels) and Group as the between-subjects factor (3 levels). There is a
> significant interaction. When examining the simple main effects, I find a
> significant difference between two of the groups at Time 2 and Time 3. My
> question is why the Univariate Tests do not show a significant effect at
> Time 2 or Time 3. What do I report and how do I explain these findings?
> Thanks!
>
>