A question about PROC MIXED

[PsycResearcher]

Hi all,

I have a question regarding PROC MIXED.

I am setting up a linear mixed model as follow:

PROC MIXED data=work.sample covtest;

     class v1 v2;

     model dv = / solution;

     random intercept / subject=v1 solution v vcorr;

     random intercept / subject=v2 solution v vcorr;

run;

v1 and v2 are categorical variables, each having more than 100 categories.

Question 1:

I assume that I have set v1 and v2 to be uncorrelated. Am I right?

Question 2:

The analysis takes me a day to complete. Is there anyway to make the syntax more efficient so that it will run faster?

Question 3:

How can I obtain the correlation between v1 and v2? Which covariance structure should I choose? (I am only interested in (1) whether v1 and v2 are correlated, and (2) the magnitude of correlation between v1 and v2.

Thank you very much for your help!

Chester