Project Summary/Abstract Over the last 15 years, an alarming chasm in health outcomes has emerged across the United States. The mortality rate of some populations?in particular working-age white adults?has increased by as much as 0.5% a year, reversing a 20-year trend of declining mortality, while mortality rates among other demographic groups in the United States and similar age populations in other developed countries have continued to decline. Disparities in health have long afflicted racial minorities and socioeconomically disadvantaged populations. Although this has motivated efforts by government and communities to reduce them, the new mortality chasm afflicting largely less-educated white populations suggests a widening gap in health by economic class. With a growing share of the nation's gross domestic product spent on health programs, this reversal of progress on mortality for any subgroup is particularly troubling. Why is this happening? While evidence suggests that elevated burdens of certain health-related behaviors or diseases (e.g. substance abuse) may play a key role, the increasing disease burden by itself cannot explain the divergence in progress between subgroups. Moreover, the causal pathways by which social determinants of health impact mortality and health differently across populations of different race/ethnicity or economic class remain poorly understood. For example, broad macro-level economic policies in the U.S. (e.g. trade) can affect economic opportunities and outlook for working-age adults; yet their impacts on health are largely unknown. And as the nation moves forward with ambitious reforms of its delivery system?rewarding improved quality of care and health outcomes at the population level?such reforms may push physicians and hospitals to focus on improving the care of disadvantaged patients the most, who often have the most room to improve, but these reforms might also exacerbate disparities in quality and outcomes via the avoidance of disadvantaged patients. Thus, understanding whether today's reforms will achieve their goals in an equitable way is a crucial task. I propose a research agenda with 2 key goals. First, I seek to identify new causal mechanisms behind the emerging disparities in health outcomes. Using macro-level economic changes as exogenous shocks to social determinants of health, I will study their impact on outcomes across race, income, and geography. Within this analysis, I will examine the associated changes in burden of disease to understand the clinical manifestations of those broader economic shocks. Second, I seek to examine whether today's reforms to the delivery system, which are designed to change the ways physicians and hospitals deliver care, can impact disparities in health by race, income, and geography. I will analyze the impact of programs that reward quality and outcomes at the physician level, such as the Medicare Access and CHIP Reauthorization Act (MACRA), as well as programs centered on incentives at the provider organization level, notably accountable care organization (ACO) models in Medicare and in privately-insured populations under age 65, on disparities in quality and outcomes.