st: Specifying categorical factors & GLMM parameter estimates

[Susan Lingle <susan.lingle@uleth.ca>]

Hi All,

I am new (1-day) to STATA and purchased it to run a specific test: a 
GLMM with a binary response variable (or logistic regression with mixed 
effects). I have a few specific questions.

(1) Categorical and ordinal variables: I re-named my categorical 
variables (which will be used as fixed factors in the GLMM) to numbers 
before pasting them into a STATA dta file. I now defined and assigned 
data labels to each number, and they appear okay.

But how can I make sure that STATA recognizes these as categorical 
variables? I see the format of ‘byte” and “%8.0g”, but does that tell me 
enough? And how can I tell STATA to distinguish between truly discrete 
variables (Europe, North America, Africa) and ordered variables (e.g., 
low, medium and high)? I assume there is no problem when there are only 
two categories (indicative), since there should be no confusion with a 
continuous or ordinal category. But I have a YEAR variable with 8 years 
(not to be ordered) and an AREA variable with four categories.

(2) Specific parameter estimates: The GLMM/binary response produces 
parameter estimates for each variable, but it gives no degrees of 
freedom (which would help me find out whether STATA is recognizing 
certain variables as categorical). It also does not produce specific 
parameter estimates, e.g., t-values with accompanying p-values for each 
level of a category. I am accustomed to seeing that output in most 
statistical programs. Advice on how to get this? Or does the absence of 
this output suggest that STATA ‘thinks’ my variables are continuous 
rather than categorical?

I have been using the menus (GUI) as much as possible.

Thanks!

Susan

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