I am trying to build some linear mixed models in SPSS, and am having a little trouble with the syntax - particularly with regards to the repeated measures aspects of my design.

I have around 40 participants, each of whom took part in 4 sessions: baseline, active, passive and control. I would like to find out if the relationship between my dependent variable - d-prime (behavioral performance on a task) and my independent variable - BOLD (brain activity) differs between session.

I think what I need to do first is specify a bunch of models i.e. a model with fixed slopes and intercepts, a model with random slopes and fixed intercepts and a model with random slopes and intercepts and compare the -2LL, but I'm struggling to specify these models correctly.

My data is arranged in a long format, and looks like this:

subject_ID session d-prime bold
1 active 3.37 .97
1 passive 3.94 .18
1 control 3.34 .31
1 baseline 3.94 .63
2 active 3.30 .83
2 passive 3.46 1.33
2 control 4.23 .62
2 baseline 1.90 -.81

1 Answer 1


I don't think you need a random slope in your design, you'll get what you need with a random intercept mixed model with a session*BOLD interaction (though I must say you have very little data for testing an interaction, are you confident you have adequate power?). But technically, I'd use the following:

MIXED d-prime BY session WITH bold
  /FIXED=session bold session*bold | SSTYPE(3)

Then, if the interaction between session and bold is significant, it suggests that bold is related to d-prime in different way in different sessions and you can for instance plot the bold - d-prime slopes for different sessions.

If you want to run an unconditional model (e.g. to report the variance component for subject), you can use

MIXED d-prime 

And then you can compute subject ICC from the Estimates for covariance parameters.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.