Re: st: Specifying categorical factors & GLMM parameter estimates

[Richard Goldstein <richgold@ix.netcom.com>]

If you have more than 2 categories, then you must form the set of 
variables yourself, either prior to estimating the model (e.g., via tab 
or via xi) or by using xi at the time of the estimation

I am not clear about what you expect Stata or any other software to do 
that is special regarding a categorical variable that is ordinal; 
perhaps you could clarify what you are expecting.

You do not show any output, but from your description it appears that 
you have let Stata default to treating each right-hand-side variable as 
continuous.

Rich

Susan Lingle wrote:

> 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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