Project Summary Black and Hispanic Medicare beneficiaries enroll at higher rates in the Medicare Advantage program but receive lower quality of care and experience worse outcomes than their white counterparts. These disparities vary markedly across plans, with some managing to deliver high quality care for traditionally marginalized populations. It is not currently known what characteristics of these plans contribute to lower disparities for Black and Hispanic enrollees. Prior work has established that Black and Hispanic patients tend to have better outcomes across various conditions when seeing physicians and other providers of the same race/ethnicity. It is not known to what extent MA plans' networks include minority physicians, and if the physician diversity in plans' networks have downstream effects on enrollee health disparities. Without an understanding of whether enrollees have access to a diverse set of providers in the Medicare Advantage program, these disparities are likely to continue. Our long-term goal is to identify strategies to reduce health disparities for Black and Hispanic enrollees in the Medicare Advantage program. The objective of this application is to develop novel methods to measure the diversity of Medicare Advantage primary care provider networks, and to determine if network diversity is an important factor in addressing health disparities. Our central hypothesis is that more diverse primary care provider networks will deliver higher quality outcomes for Black and Hispanic enrollees. The rationale that underlies the proposed research is that publicly available measures of network diversity may help health plans better understand their own networks and help minority patients make enrollment decisions that lead to improved downstream outcomes. Using a unique set of national Medicare Advantage network data linked with self-reported provider race/ethnicity, we propose two specific aims: 1) to develop a measure of primary care physician network diversity, and 2) to determine if access to diverse primary care physician networks is associated with a reduction in disparities and improved outcomes for minority patients. This study is innovative in that it will employ a novel linkage of provider network and race/ethnicity data to measure the diversity of provider networks and is one of the first studies on what contributes to heterogeneity in disparities across plans. Upon completion of this work, we expect our contribution to be a newly developed metric of provider network race/ethnicity that can better inform stakeholders on the diversity of provider networks and a better understanding of the role that diverse provider networks play on the outcomes of minority enrollees. This contribution will be significant as over 3 million Black and Hispanic Medicare beneficiaries receive their care from Medicare Advantage plans and we have little to no understanding of the providers they have access to and whether this access is a driver of...