Health Insurance Coverage and Outcomes: What Research Shows About the Uninsured

Health insurance coverage is a fundamental determinant of access to healthcare in the United States, where most care is financed through a combination of private insurance, government programs, and out-of-pocket payment. Approximately 25 to 30 million Americans lack health insurance at any given time, a proportion that declined significantly following the Affordable Care Act's expansions of Medicaid and the insurance marketplace, but that remains high relative to peer nations that have achieved universal coverage through different mechanisms. Research on what insurance coverage means for health outcomes, healthcare utilization, and financial security documents effects that are consistent in direction if complex in detail. The Oregon Health Insurance Experiment, conducted when Oregon expanded its Medicaid program by lottery in 2008, provided the closest thing to a randomized controlled trial of health insurance coverage available in the United States context. Researchers tracked a group that won Medicaid coverage through the lottery and a control group that did not over two years. They found that Medicaid coverage increased healthcare utilization, reduced financial hardship from medical bills, and improved mental health outcomes. Effects on physical health outcomes, including blood pressure, cholesterol levels, and blood glucose, were positive in direction but not statistically significant after two years, which critics interpreted as evidence that coverage did not improve physical health and proponents interpreted as reflecting insufficient follow-up time. Quasi-experimental research exploiting variation in Medicaid eligibility, state-level coverage expansion, and the timing of the Affordable Care Act's provisions has found more consistent evidence of coverage effects on physical health outcomes. Studies find that Medicaid expansion is associated with reduced rates of diagnosis at late disease stages for cancer, reduced cardiovascular mortality, reduced maternal mortality, and lower overall mortality rates. These effects are larger than those found in the Oregon experiment and are consistent with evidence that longer follow-up periods are needed for coverage to produce detectable effects on chronic disease and mortality outcomes. Financial protection is among the most clearly documented effects of health insurance. Research finds that uninsured individuals are substantially more likely than insured individuals to forgo needed care due to cost, to delay care until conditions worsen, to experience medical debt and bankruptcy, and to use emergency departments as primary care. Medical debt affects tens of millions of Americans and is a leading cause of personal bankruptcy. Research on insurance coverage expansions consistently finds reductions in financial catastrophe from medical bills among newly covered populations. Emergency department use by uninsured individuals reflects their lack of primary care access and their legal right to emergency care regardless of insurance status. Research on emergency department utilization finds that uninsured individuals use emergency departments more than insured individuals for conditions that could have been managed in primary care settings. Coverage expansions reduce emergency department use for ambulatory-care sensitive conditions, consistent with the view that primary care access reduces inappropriate emergency utilization. Racial disparities in insurance coverage are significant and documented. Black and Latino Americans have higher uninsurance rates than white Americans, reflecting a combination of lower rates of employer-sponsored insurance, higher concentrations in low-wage jobs without benefits, state-level variation in Medicaid expansion in states with large minority populations, and immigration status restrictions on coverage eligibility. Research on coverage expansion finds that racial minority populations show the largest absolute gains in insurance from expansion, but persistent structural barriers mean that coverage gaps remain. The Affordable Care Act's coverage expansions produced the largest reduction in the uninsurance rate in American history. Research on the ACA's effects finds significant increases in coverage, reductions in uncompensated care costs for hospitals, and improvements in access to care in expansion states compared to non-expansion states. The law's Medicaid expansion, which was made optional by the Supreme Court's 2012 decision, has been adopted by most but not all states, producing a coverage disparity between expansion and non-expansion states that research finds has affected health outcomes. Uncompensated care costs, which are incurred by hospitals when uninsured patients receive care they cannot pay for, represent a significant financial burden on the healthcare system. Research on uncompensated care finds that it falls disproportionately on safety net hospitals serving low-income and uninsured populations, and that coverage expansion significantly reduces this burden. The reduction in uncompensated care cost is one mechanism through which coverage expansion improves hospital financial stability in low-income communities.