Dear Koen, Thanks for your reply but this solution allows to model multiple classifications but not multiple memberships : an ego may belong to two different groups of the same classification variable. Ego may be member of, say, triad 1, and of triad 2, etc. To take your example, a student may belong to two different classes ( for whatever admin reasons). In addition some egos may have juste one membership, whereas others may have many more: the pattern of memberships may be very different from one ego to another. In GLIMMIX these complexities can be handled with the « EFFECT » statement. How to do the same in PROC BGLIMM ? Thanks for the guidance. Vincent
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