how to enter categorical variables in genlin models

Posted by mpirritano on Jun 08, 2009; 3:21pm
URL: http://spssx-discussion.165.s1.nabble.com/Paired-test-for-3-variables-tp1089169p1089171.html

I know that when I enter categorical variables into a logistic
regression with pasw I do not need to enter in all dummy or effect coded
versions of the variable. Correct me if I'm wrong. In OLS regression,
yes, you do need to enter all dummy variables.

The question is: In genlin do you need to enter all dummies, or if you
enter a categorical as a factor then is all taken care of? I notice that
I do get one fewer effect than the total number of categories, as I
would with dummies. If genlin takes care of the coding when I enter the
categorical variable what type of coding does it use (effect, dummy)?

Actually I've just noticed that when I request contrast coefficient (L)
matrices the matrices look like effect coding. Kind of annoying that
it's so inconsistent. Sometimes you need to do the coding yourself
(regression), sometimes you don't (logistic regression, genlin)? Or does
it hurt if you do enter them manually for logistic or genlin?

Please confirm.

Thanks for all the help folks!

matt

Matthew Pirritano, Ph.D.
Research Analyst IV
Medical Services Initiative (MSI)
Orange County Health Care Agency
[phone]

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