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Nested random effects in GLIMMIX

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Nested random effects in GLIMMIX

Hello,

I have two categorical variables (A and B) that I want to add as Random factor in GLIMMIX. A has 4 categories and B has 44. Finally B is nested in A.
When I added as random factor, the model results said that "Estimate G matrix is not positive definite". How can I solve this problem? Did I add the variables in a correct way??

proc GLIMMIX data=Resumen;
class A B Cat;
model total = intra flux Cat length / dist=poisson link=log solution;
random B B(A);
run;
Respected Advisor
Posts: 2,655

Re: Nested random effects in GLIMMIX

While this may not solve the problem completely, note that the statement:

random B B(A);

specifies factor B twice. That may be the source of the error message.

Try

random A B(A);

This should specify A as a random effect, and B within A as a second effect.

Good luck.
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