Back to Annual Meeting Page		American Public Health Association 133rd Annual Meeting & Exposition December 10-14, 2005 Philadelphia, PA

Abstract #107474

Linda G. Marc, ScD, MPH, MS¹, Lisa F. Berkman, PhD¹, Charles Lewis, PhD², and Marcia A. Testa, MPH, PhD³. (1) Department of Society, Human Development and Health, Harvard School of Public Health, 677 Huntington Avenue, 7th FLoor, Boston, MA 02115, 617-421-0167, linda.marc@post.harvard.edu, (2) Department of Psychology, Fordham University, Rose Hill Campus, Dealy Hall 226G, 441 East Fordham Road, Bronx, NY 10458, (3) Biostatistics, Harvard School of Public Health, 655 Huntington Ave., Boston, MA 02115

Differential item functioning (DIF) is used to evaluate if there is a systematic difference in the probability of instrument item-response across population groups. The 20-item HIV Symptom Distress Index measures HIV symptoms in antiretroviral clinical trials. In the study population under investigation, the effect of education, gender, and race/ethnicity on the properties of the index are uncertain.

Although the intended purpose of the index is to identify and describe individual symptoms that may reflect underlying clinical phenomenon, the measurement of DIF requires the assumption of unidimensionality. Using factor analysis, preliminary results show that all items are related to a single common factor (total communality 87.4%). By creating a total index summary score (alpha=0.89), we performed an exploratory regression analyses to identify associations among demographic and clinical variables. Item-response analyses show the presence of uniform and non-uniform DIF within demographic subgroups (p <0.05).

Data are from the baseline measures of a clinical trial which enrolled antiretroviral-naïve individuals infected with HIV-1. Educational attainment (EA) was measured as an ordinal categorical variable.

In an effort to improve patient-centered care and eliminate health disparities, the assessment of DIF will advance our knowledge about individual symptoms and their impact on specific patient populations.

Learning Objectives:

• At the conclusion of the session, the participant (learner) in this session will be able to apply differential item functioning techniques on scales and instruments used in health outcomes research.

Keywords: Methodology,

Presenting author's disclosure statement:

I wish to disclose that I have NO financial interests or other relationship with the manufactures of commercial products, suppliers of commercial services or commertial supporters WITH THE EXCEPTION OF GlaxoSmithKline, Novartis and Pfizer.