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From | "Vahidnia, Farnaz" <FVahidnia@bloodsystems.org> |
To | "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |
Subject | st: nlogit for single observation data using STATA 12 |
Date | Mon, 5 Aug 2013 21:34:38 +0000 |
Hello, I am trying to fit a nested logit model to estimate OR of being an HIV case by gender for certain risk factors. I don't want to stratify be gender because most independent variables are shared between male and female, and I want to stratify only on variables related to sexual risk behavior. I only have one observation per subject and am using STATA 12. The gender specific independent var in my data is sexual orientation (sexorientlife) with three levels: 1=Heterosexual, 2=homosexual and 3=bisexual I created the tree structure using: nlogitgen gender=male (male:1, female: 0) nlogitgen sexorient=sexorientlife (hetero: 1, homo: 2 3) My tree structure looks like this: tree structure specified for the nested logit model gender N sexorient N k ------------------------------------ male 1238 --- hetero 1120 439 +- homo 118 105 female 1202 --- hetero 1098 368 +- homo 104 60 ------------------------------------ total 2440 972 My dependent var is "hivcase", binary, 0 for controls 1 for cases. The model look like: . nlogit hivcase ageyear lowincome black multiplepartner || gender: || sexorient:, case(study_number) noconstant note: 1485 cases dropped because they have only one alternative no cases remain after removing invalid observations I guess the problem is that "nlogit requires only that hierarchy be maintained for all cases." Which is not true in my data, as a subject does not have a choice to multiple sexual orientations. In other words my choices are mutually exclusive. Another problem I guess is that IIA is a property is violated as the odds of choosing one alternative over another (sexual orientation) is not independent of the other alternatives. I am thinking about considering gender as a group option, to make data look like 2 subjects with ~ 1200 observations per subject. I appreciate any help or comment. Thanks, Farnaz * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/