From: Ryan on
For those interested:

I found an article that describes how to account for partial nesting
in linear mixed models.

Bauer, D. J., Sterba, S. K., & Halfors, D. D. (2008). Evaluating group
based interventions when control participants are ungrouped.
Multivariate Behavioral Research, 43, 210–236.

The authors were kind enough to provide a step-by-step explanation of
how to account for partial nesting in PROC MIXED at the following
website.

http://www.unc.edu/~dbauer/manuscripts/BauerSterba_appendix_SAS.pdf

Best,

Ryan