PROJECT SUMMARY/ABSTRACT People with severe mental illness (e.g., schizophrenia, bipolar disorder; SMI) are a socially marginalized population with up to ten times increased likelihood of being diagnosed with HIV compared to the general United States population. The parent grant (R01-MH112420) aims to investigate the increased HIV transmission risk, low testing rate, and potential HIV treatment gaps for people with SMI using a large, geographically diverse national retrospective longitudinal Medicaid cohort. The outcomes assessed by the parent grant, however, may be modified by membership in intersecting categories of social marginalization. Single-axis interventions that do not consider heterogeneities among vulnerable populations may not be effective in improving outcomes and achieving epidemic control. Therefore, research is needed to identify and assess the magnitude of outcome inequalities among the riskiest intersectional positions. Leveraging twelve years of Medicaid data (2001 through 2012), the major goal of this research is to assess the existence and magnitude of outcome inequalities along the HIV continuum of care, with respect to intersecting categories of social marginalization (e.g. schizophrenia diagnosis, race/ethnicity, sex, intravenous drug use, etc.). The diversity supplement seeks to provide mentored theoretical and methodological training for the candidate in the area of quantitative intersectionality research. The proposed career development aims are: (1) to develop foundational knowledge in intersectionality as a theoretical framework; and (2) to develop expertise in quantitative intersectionality research methods. Aligned with the career development objectives, the research goals of the proposed study are to: (a) research the cutting-edge quantitative intersectionality approaches to assess the existence and magnitude of HIV outcome inequalities within a large administrative database; (b) examine differential rates of HIV testing by intersecting categories of schizophrenia diagnosis, sex, age, history of intravenous drug use, and race/ethnicity in the R01 parent grant retrospective cohort; and (c) examine differential rates of treatment for HIV by intersecting categories of schizophrenia diagnosis, sex , age, history of intravenous drug use, and race/ethnicity in the R01 parent grant retrospective cohort. The evidence generated from this work could identify the riskiest intersectional positions to inform targeted, cost- effective, interventions to improve HIV testing and care outcomes among those most vulnerable. Additionally, the foundational knowledge of intersectionality as a theoretical framework, paired with the application of quantitative intersectionality methods to a large administrative data set, will position the candidate to have an impactful career as an independent investigator generating rigorous quantitative evidence demonstrating health inequities among socially marginalized populations.