BookmarkSubscribeRSS Feed
Calcite | Level 5



I have a dataset with a continuous outcome variable and 3 treatments (1 of which is placebo). I have about 60 observations in my dataset; 60 subjects each of which got 1 treatment and was measured once - the dataset is balanced but measurements were taken in blocks of days but only 2 measurements were taken each day (incomplete blocks?). I need to include the block in  my model as a random effect. I am trying to get the effect of the drug and im running a proc mixed with a random block effect, but i am not getting an anova table and am getting an error that the "Estimated G matrix is not positive definite." Can anyone tell me what I am doing wrong? Thank you.

Jade | Level 19

Please share your PROC MIXED code and enough of your data to enable some trouble shooting.  I suspect that you may have misspecified the random effect, as the message 'Estimated G matrix is not positive definite' means that at least one variance parameter is being set to zero.  There are a couple of ways around this, but it depends on design, data structure and code.


Steve Denham



Registration is open! SAS is returning to Vegas for an AI and analytics experience like no other! Whether you're an executive, manager, end user or SAS partner, SAS Innovate is designed for everyone on your team. Register for just $495 by 12/31/2023.

If you are interested in speaking, there is still time to submit a session idea. More details are posted on the website. 

Register now!

What is Bayesian Analysis?

Learn the difference between classical and Bayesian statistical approaches and see a few PROC examples to perform Bayesian analysis in this video.

Find more tutorials on the SAS Users YouTube channel.

Get the $99 certification deal.jpg



Back in the Classroom!

Select SAS Training centers are offering in-person courses. View upcoming courses for:

View all other training opportunities.

Discussion stats
  • 1 reply
  • 2 in conversation