Hello,   In this paper, the analysis of domains, sometimes called subpopulations, is discussed. The examples are on ordinary least squares regression and logistic regression , but maybe you can 'extrapolate' to GLIMMIX. Analysis of Complex Survey Data with SAS® Christine R. Wells, Ph.D., UCLA, Los Angeles, CA https://www.lexjansen.com/wuss/2017/133_Final_Paper_PDF.pdf   Look also here : https://support.sas.com/rnd/app/stat/procedures/SurveyAnalysis.html All SURVEYxxxxx procedures support domain analysis / subpopulation analysis.   BR, Koen ... View more