REPEATED MIXED MODELS-post hoc tests/contrasts

Posted by Alexandra on Nov 24, 2014; 4:01pm
URL: http://spssx-discussion.165.s1.nabble.com/REPEATED-MIXED-MODELS-post-hoc-tests-contrasts-tp5728007.html

Hello!
  I am studying the effect of trait anxiety on working memory efficiency (RT) and accuracy and I need some help with using LMM.
  The working memory task had four blocks varying in list length presentation, presented to each subject (1,2,3,4 words to recall). I was thinking to run a LMM with a random intercept with RT / ACC as a DV, list length as a repeated within factor (or covariate?), anxiety as a covariate. Therefore, I have the fixed effects: list length, anxiety and list length * anxiety interaction and at random effects, include intercept and Subjects (is that ok?)

So I have the following variables:
DV: efficiency score/ accuracy for every list length (continuous-within repeated measure)
IV: list length (categorical)
Covariate: trait anxiety (continuous)
*each repeated measure (level 1) is within subject category (level 2). I already put the data in long format.

My questions are:
1) in order for SPSS to know it's repeated data, should I choose from the first window of LMM, Subject ID at subjects and list length as a repeated measure? Or is it enough subjects and then include the random intercept?
2)   how do I compare between list lengths? I want to show for example that list length’s effect is more significant at list length 4 that list length 1. So there are sign differences between lists. Should I use post hoc tests? Also, how do I compare which list length is more affected by it’s interaction with anxiety? Is there a contrast option in LMM for that?
 
Thanks a lot! any kind of input would be very very helpful...
Alexandra