Hi, I have a data set where I have a dependent variable Y , a treatment variable (Trt) and set of random factors z1(10 levels), z2(2 levels) and z3(2 levels) such that z3 is nested in z2 and z2 is nested in z1 I am using proc mixed to analyze this data. Code below : proc mixed method=REML; class trt z1 z2 z3; model y = trt; random z1 z2(z1) z3(z1 z2); run; The problem is the covariance estimate for z2 comes out as zero. I am wondering why I am getting such an estimate. Any help/insight would be appreciated. PS: I have also tried other methods i.e. MIVQUE0 , type 1 and type 2 and ML Regards, Arunava
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