BookmarkSubscribeRSS Feed
🔒 This topic is solved and locked. Need further help from the community? Please sign in and ask a new question.
fengyuwuzu
Pyrite | Level 9

When I ran a mixed model, I got a note of

NOTE: Convergence criteria met but final hessian is not positive definite.

 

I added "parms /old" and still got he same note. Is this because I used "type=cs" in the second random statement?

How to take care of this note message, or having this note does mean my model is not valid? Thanks

 

proc mixed data=addm1 method=reml;
   class TRTPN(ref='1') VISITNUM(ref='1') SUBJID;
   model CHG=TRTPN VISITNUM TRTPN*VISITNUM/solution;
   random intercept/subject= SUBJID type=un;
   random intercept/subject=pknum(SUBJID) type=cs;
   lsmeans TRTPN/pdiff adjust=SCHEFFE;
   parms /ols;
run;
1 ACCEPTED SOLUTION

Accepted Solutions
Rick_SAS
SAS Super FREQ

There are several possible reasons, which are discussed in the excellent paper "Tips and Strategies for Mixed Modeling with
SAS/STAT Procedures" (Kiernan, Tao, and Gibbs, 2012).  In my experience, a common reason is that the model does not fit the data, either because it is misspecified or because the sample is too small.

 

View solution in original post

2 REPLIES 2
Rick_SAS
SAS Super FREQ

There are several possible reasons, which are discussed in the excellent paper "Tips and Strategies for Mixed Modeling with
SAS/STAT Procedures" (Kiernan, Tao, and Gibbs, 2012).  In my experience, a common reason is that the model does not fit the data, either because it is misspecified or because the sample is too small.

 

fengyuwuzu
Pyrite | Level 9

Thank you Rick. I read this paper this morning, and the idea to include 

parms /ols;

is from this paper. I will read it more carefully 

 

Probably due to the small sample size, and we have 5 arms.  

Ready to join fellow brilliant minds for the SAS Hackathon?

Build your skills. Make connections. Enjoy creative freedom. Maybe change the world. Registration is now open through August 30th. Visit the SAS Hackathon homepage.

Register today!
What is ANOVA?

ANOVA, or Analysis Of Variance, is used to compare the averages or means of two or more populations to better understand how they differ. Watch this tutorial for more.

Find more tutorials on the SAS Users YouTube channel.

Discussion stats
  • 2 replies
  • 14999 views
  • 1 like
  • 2 in conversation