Number of effective subjects - empirical SEs from proc mixed

[marcaya]

I am trying to fit a three level model: observations ("t") nested in subjects ("id"), subjects cross-classified into municipalities -people have moved over time in my study so I can't use a simple nested structure ("MuniID"). I'd like to compute empirical rather than model-based standard errors for my fixed effects, but when I specify the empirical option in PROC MIXED, I get a warning that I only have one effective subject. The dimensions table says I only have one effective subject, though the class level information is correct - I have 5 waves in 1,741 people in 195 towns.

I'm confused about why my dataset is read by SAS as having only one effective subject and how I can get the empirical standard errors I need. Anyone have any thoughts?

Any advice would be greatly appreciated!

Code:

proc mixed data = obese method = ml;

class ID t MuniID RACE SEX;

model BMI= edu inc age RACE SEX density time time*time pctpov fcrate/ solution;

repeated t/type =un subject=ID;

random intercept / subject=MuniID;

run;

Output

Dimensions
Covariance Parameters	16
Columns in X	22
Columns in Z	195
Subjects	1
Max Obs Per Subject	20232

Class  Level Information
Class	Levels
ID	1741
t	5
MuniID	195
RACE	5
SEX	2