You can add WAVE to your RANDOM statement --   proc glimmix data=AggData method=quad noclprint; title 'Time Null model'; class PARTID; model Aggression = Wave / dist=nb link=log s; random intercept wave / TYPE=UN subject= PARTID; run; The Covariance Parameter Estimates table provides the estimates and and standard errors, so you could have a sense of how significant the estimates are. If you wanted to have a p-value, you can use the COVTEST statement in PROC GLIMMIX. https://go.documentation.sas.com/doc/en/pgmsascdc/v_034/statug/statug_glimmix_syntax06.htm For example, covtest zeroG;   Hope this helps, Jill ... View more