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From |
Constantine Daskalakis <C_Daskalakis@mail.jci.tju.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Statistical/Stata question |

Date |
Tue, 17 Feb 2004 21:07:42 -0500 |

At 08:26 PM 2/17/2004, Jose Maria wrote:

Dear Statalisters: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.

Regards,

Jose Maria

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.

CD

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________________________________________________________________

Constantine Daskalakis, ScD

Assistant Professor,

Biostatistics Section, Thomas Jefferson University,

211 S. 9th St. #602, Philadelphia, PA 19107

Tel: 215-955-5695

Fax: 215-503-3804

Email: c_daskalakis@mail.jci.tju.edu

Webpage: http://www.jefferson.edu/medicine/pharmacology/bio/

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**Follow-Ups**:**Re: st: Statistical/Stata question***From:*Jose Maria Pacheco de Souza <jmpsouza@usp.br>

**Re: st: Statistical/Stata question***From:*Richard Williams <Richard.A.Williams.5@nd.edu>

**References**:**st: Upcoming NetCourses***From:*"Shannon Driver, StataCorp" <sdriver@stata.com>

**st: Statistical/Stata question***From:*Jose Maria <jmpsouza@usp.br>

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