can the variable variance variance be fixed which statement in sas proc mixed is used to fix the residual variance? what is the sas proc mixed model how to constrain covariance how to constrain variance in mixed model how can sas mixed model be used how to constrain variance in sas mixed can you constrain variables in sas mixed data how to constrain the variances of an average in sas mixed model? what is the variance of sas mixed data how to constrain variance in sas mixed model sas proc mixed test results how do you constrain covariance how to constrain covariance in sas can a variance test in sas be used how to constrain residual variance on a model sas mixed how to constrain variance in sas proc? which statement to use when estimating the variance in sas mixed model how do we find the variance of the variable when we use a parms statement? is variance a covariance in sas