class variable question

[proctice]

I put a class variable with 12 levels into a model and I got 11 parameter estimates, but one of them is 0 with zero degrees of freedom and it is not my reference level.  Any idea why this happens?  It doesn't happen to my class variable with 5 levels.  Thank you. 

[Tom]

It probably depends on what PROC you are using.

Can you show the code you used?  Perhaps some of the statistics the proc generated?

[proctice · Accepted solution]

Thank you.  I think I figured it out.  There was another categorical variable with 2 levels that when cross-tabbed with my 12 level categorical variable had lots of empty cells.  Sorry to bother you. 

I think this is called complete separation.  I was using Proc Genmod.