Virginia,
What commands are you running for the two analyses?
From what you say below, the difference is one is paired and the other is not.
IF that is the case, it would suggest that pairing matters.
However, list members can help better with clearer details (preferably syntax) about what was run.
Some thoughts to consider….
Is it logical to pair cases in your groups? i.e. height across time for children is very logical to pair and illogical not to pair cases-in this case the overall
groups may not differ at each time, but pairing takes into account the variation of values within each sample.
Apparently your groups have different variances. (i.e. continuing the height example, one group may be same grade students (low variance) and another may be
multiple grade students (high variance).
Is that difference in variances expected or unexpected? (Why?)
Is the difference in means meaningful? (What does it mean?)
And a key consideration which may be yours or someone else’s: Does that matter? (So what?)
Melissa
From: Virginia Tompkins [mailto:[hidden email]]
Sent: Wednesday, June 04, 2014 10:42 AM
To: Ives, Melissa L
Subject: Re: [SPSSX-L] Simple Main Effects Pairwise Comparisons vs Univariate Tests
Hello Melissa,
I'm not sure if I understand what you are asking, but I don't think that is the case. The pairwise comparisons are comparing the mean differences between each of the groups at each of the 3 time points with a significant difference in the
means of two of the groups at Time 2 and Time 3. The univariate tests present the F and p-value for each of the 3 Times, but none is significant. I suppose it is possible that there is a significant interaction, with some of the group comparisons at some of
the time points being significant, without each time point having a significant group effect? Does that make sense? If that is the case, how do I report the findings of the simple main effects and the univariate tests?
Thanks!
Virginia
On Wed, Jun 4, 2014 at 9:30 AM, Ives, Melissa L <[hidden email]> wrote:
You'll need to say more about what you actually used to examine the simple main effects
Could it be that the former is looking at the slope between times while the latter looks at the actual state at the time point?
Melissa
-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of statshelp
Sent: Tuesday, June 03, 2014 7:29 PM
To: [hidden email]
Subject: [SPSSX-L] Simple Main Effects Pairwise Comparisons vs Univariate Tests
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!
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