My dataset consists of 4 variable:
values, dil, exp and sample. There are 170 values obtained for variable values; there are 5 levels for the variable
dil, 10 levels for the variable
exp and 5 levels for the variable
I fitted a mixed model in
SAS to find the variance component estimates:
proc mixed; by sample; model values = dil; random exp; run;
dil is fixed and
experiment is random.
When I fit the model, the covariance estimate for for
exp is zero. It says that
"Convergence criteria met but final hessian is not positive definite".
Can anyone give some help on this? Thank you!
Also there are a few
na values in the dataset.