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Re: st: Statistical/Stata question
At 08:26 PM 2/17/2004, Jose Maria wrote:
It isn't silly at all.
I think it is more of a statistical question, but may I ask it:
If I have a categorical variable (letīs say with 4 categories) and run
the logistic regression _logistic depvar category2 category3 category4_, I
get the odds ratios relating each of the 2,3,4 categories against the
category1 reference, with straigthway interpretation. What is the
interpretation if I do _logistic depvar category3 category4_?
Sorry if it is a silly question.
In effect, you are forcing the first two categories (1 and 2) to have
exactly the same odds (probability) for the event. In other words, you are
constraining the odds ratio for category2 vs. category1 to be exactly equal
to 1. As a consequence, the comparison of category3 to category1 has the
same odds ratio as the comparison of category3 to category2 (and similarly
for category4). For the purposes of the model, there are only 3 categories:
a combined 1/2 category, category3 and category4.
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Biostatistics Section, Thomas Jefferson University,
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