6th January 2014 at 10:02 pm #1294Kerwin OlfersMember
I’m sure this has been asked and answered before, but I just can’t seem to find a complete answer anywhere, so I’d greatly appreciate a nudge in the right direction!
I’m running a Mixed Model ANOVA with the following factors:
Within-subjects: Session(2), Task condition1 (2), Task condition2 (2)
Between-subjects: Group (3)
Following the Discovering Statistics Using SPSS book, I’m able to interpret interaction of Session x Task conditions, using simple contrasts.
However, I’m a bit at a loss of how to do this for Session x Group, and Session x Group x Task condition1 interactions, as there are no contrast specifications for Group.. I can see that the interactions is significant, I just don’t know between which groups the difference are significant. (As the book only shows the situation with a 2-level between-subjects variable)
What would be the appropriate course of action here?
– Would it suffice to run the Mixed Model three times, just excluding 1 of the three groups each time?
– Should I create difference scores, and then do a regular ANOVA?
– Is there a different, more suitable approach?….
Many thanks in advance!
Kerwin7th January 2014 at 6:20 pm #1296Dave CollingridgeParticipant
You may not have set up your variables properly. You need the following 9 variables in your data set where “s” represents session and “t” represents task condition.
In SPSS go: analyze -> GLM -> repeated measures -> enter the following within subjects variables (number of levels shown in parentheses: session(2), task1(2), task2(2) -> enter a name for your outcome variable -> click define and move group into between subjects box and all other variables into the within subjects box (there should be slots for all 8 variables -> in contrasts change all contrasts to simple.
This will produce all main effects, 2-way, and 3-way interactions in the output file.7th January 2014 at 7:58 pm #1295Kerwin OlfersMember
Thank you for your reply!
I think I’ve set up the variables correctly, just to clarify, the within-group contrast work fine, I get all the interactions. However for the within x between interaction, say for the interaction Session x Group, I would get as a contrast:
Session (level 1 – level 2) x Group
That is, it tells me there is a difference between session 1 and session 2 on the scores of the Different groups, but it does not give contrasts nor post-hoc comparisons to see between which of the 3 Groups the difference is significant.
Thank you again,
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