PROJECT SUMMARY/ABSTRACT Despite that the US spends much more on healthcare than other high-income countries, the health and life expectancy of US working-age adults has declined, losing ground further to their peers in other countries. Identifying those most at risk for worsening health and determining the key factors contributing to the widening health disparities in the US population is critically important and timely. The overarching goal of this project is to clarify the multi-level factors in determining US midlife health, focusing on disability and cognitive functioning outcomes. We will first focus on within-US comparison determining the role of place-specific contextual factors in disability and cognitive functioning among working-age adults in the US. We will use a quasi- experimental approach to enhance detecting marginal effects attributable to place-level vs. individual- level factors; we compare adults with similar individual-level characteristics and resources but living in areas with different place-level contexts. We will examine contextual factors of multi-level geographic units such as tract-level social vulnerability and built environment, county-level social programs and resources, and state-level social protection and healthcare policy. We will also capitalize on life-history data that provide residential histories over the entire life course to help understate the level of exposure and differential effect by life stage. We will then identify factors contributing to the relative position of US midlife disability and cognitive functioning compared to other high-income European countries. We will use harmonized survey data from the Health and Retirement Study (HRS), English Longitudinal Study of Ageing (ELSA), and Survey of Health, Ageing and Retirement in Europe (SHARE). We will assess the extent to which national-level economic inequality, healthcare system, and social protection policies affected the relative position of the US among low- vs. high-SES adults. We will then examine the extent to which local-area factors contribute to the difference in the outcomes across countries by leveraging and extending the study team’s novel procedure to harmonize local-area contextual data across countries and link the contextual data to each survey. This study will contribute to clarifying socioeconomic, physical, and institutional factors for geographic variation in midlife health by intersecting multi-level contextual factors with individual-level socioeconomic characteristics. The project will also advance data for the comparative assessment in cross-country health disparity by generating the local-area data harmonized across high-income countries, which will be released in full compliance with confidential data protection policies. 1