proc mixed- zero covariance estimates

archnova — Sun, 15 Jul 2012 07:20:32 GMT

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

Re: proc mixed- zero covariance estimates

SteveDenham — Mon, 16 Jul 2012 12:39:13 GMT

It most likely means that there is insufficient variability remaining after fitting z1 to get a positive estimate with the data you have in hand. The only real solution is the most expensive one--obtain more data.

Steve Denham

topic Re: proc mixed- zero covariance estimates in SAS Procedures

proc mixed- zero covariance estimates

Re: proc mixed- zero covariance estimates