SPSS - MIXED Specifying covariate at level 2 or higher?

bramv

New Member
Hi there,

Hopefully I'm not posting a stupid question, but here goes:

I'm reading up on doing multilevel analyses in SPSS and following some 'tutorials' and there is one thing that seems weird to me:

As far as I can tell, you do not specify fixed effects for level 1 any different than for level 2 (or 3 etc.). It seems you just have to add the variable name to the FIXED argument, and that's it. Is that correct?

Very simple example: measurements done on students in classes with random intercepts only:

dv = dependent variable
level1cov = covariate measured at level 1 (student level)
level2cov = covariate measured at level 2 (class)

MIXED dv WITH level1cov level2cov
/FIXED = level1cov level2cov | SSTYPE(3)
/METHOD = REML
/PRINT = SOLUTION
/RANDOM INTERCEPT | SUBJECT(class) COVTYPE(VC).

So first question: is this the correct way of specificying the fixed effects for both levels?

And second question: if this is correct, how does the model 'know' on which level the variable is measured? Or does it not need to know that? I guess I don't fully understand... can someone explain a little bit about this? Thanks!

New Member
Hi all,

I am facing exactly the same problem. Does anyone have an idea? Or did you, @bramv , figure it out already?

Any assistance would greatly be appreciated, thanks!

spunky

Doesn't actually exist
SPSS (much like R, STATA and SAS) neither use nor recognize this "Level 1" vs "Level 2" language. That's a direct consequence of the Raudenbush and Bryk software and the whole notation/framework they developed for mixed-effects models. If you want to use SPSS to fit a mixed-effects model, you need to know how to specify a mixed effects equation of the form $$y = X\beta + Zu +\epsilon$$ where the $$X\beta$$ are the fixed effects and $$Zu$$ are the random effects.