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09-24-2008 03:46 AM

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;

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??

class A B Cat;

model total = intra flux Cat length / dist=poisson link=log solution;

random B B(A);

run;

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09-26-2008 08:48 AM

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.

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.