Hi everyone,
I'm having a problem with a multilevel model, I'm running it in SAS and I
got a warning message:
WARNING: The final Hessian matrix is not positive definite, and therefore
the estimated covariance matrix is not full rank and may be unreliable. The
variance of some parameter estimates is zero or some parameters are linearly
related to other parameters.
I'm trying to fit a model with a binary output and logit link, this is the
program:
proc nlmixed data=Angie.Maxdata tech=trureg;
parms beta=19.53 beta1=2.92 S1=0, S2=0,S3=0;
eta=beta + beta1*logmaxi+u;
expeta=exp(eta);
p=expeta/(1+expeta);
model i~binary(p);
random u ~normal (0,0) subject=POP;
predict p out = uniq_pred_loc;
run;
I'll really appreciate if any of you could help me with some suggestions.
This is the first "real" multilevel model I'm doing and I'm not sure what
I'm doing wrong.
Thanks,
|