I am running a proc glimmix model for a multi-site study, we have only three sites, each site has about 400-700 patients, the outcome is a binary variable. First I would like to see if the random site (siteID) effect is necessary in the model. Here are my codes. proc glimmix data=SubjectPQ_combine method=quad; class SiteID; model CSPrepQual2CAT (event='0')=/dist=binary link=logit solution; random intercept/subject=siteID type=vc; covtest zeroG/wald; title1 'GLIMMIX model-site as random effect'; title2 'Test variance of random effect'; run; I am not sure how to interpret the covtest zeroG/wald results, although I read the proc Glimmix procedure, covest. The "covariance Parameter Estimates" indicates a p-value 0.148, however, the "Tests of Covariance Parameters Based on the Likelihood" indicated a p-value <0.0001. My understanding is that based on the first p-value, there isn't significant variance for random effect. However, the second p-value means there is significant variance for random effect. Where am I wrong? Thank you in advance.
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