Tuesday, March 07, 2006

st: Assessing true odds ratios in logistic regression models with interaction terms


I'm having a fairly knotty problem with stata. Let me give you a background before I ask the questions:

I have one outcome variable - screening test - yes or no

I have four independent variables - gender (male, female), income (3 categories - low, medium, high), age (4 categories in 5-year intervals), education (3 categories - low, medium, high)

There are three interactions that are signficant on univariate analysis - gender*income, gender*educn, gender*age category.

The final model should look like this

.xi: logisitic screentest gender educn income agecat i.gender*i.educn i.gender*i.income i.gender*i.agecat

Now this will provide the following co-efficiencts

gender_1 income_2 income_3 educn_2 educn_3 agecat_2 agecat_3 agecat_4 _gen_educn2 _gen_educn3 _gen_income2 _gen_income3 _gen_agecat2 _gen_agecat3 _gen_agecat4

Now, if i want the true odds ratios for gender (ie. male vs. female), what command do I use to estimate this from the model?

I want my output table to look something like this...

Income OR for male vs. female ---------------------------------------- Income1 OR1 Income 2 OR2 Income 3 OR3 ----------------------------------------

This OR should be adjusted for age, gender, educn, and the interaction between gender and age, and gender and educn.

Can someone help me with this problem? Does it have a solution in stata?

Thanks, Ashwin

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