The adverse effects of income inequality on persistent health disparities are well documented, but cross-national differences in the interaction of income inequality and health system performance have been underexamined. 

A new study addresses this gap by comparing health system performance and income-related inequalities between the United States and South Korea over a decade. The two countries, both members of the Organisation for Economic Co-operation and Development (OECD) with high poverty rates and vastly different health system structures, serve as informative testbeds for how policy and institutional contexts shape the magnitude and nature of health inequalities. 

The cross-national study, published in JAMA Health Forum, finds that income remains a powerful determinant of performance in both the U.S. and Korean health systems, despite their structural differences. It reveals consistent patterns of income-related health inequalities across multiple domains, with disparities significantly more pronounced in the United States.

“The findings suggest that structural and systemic policy efforts are needed to address income-based health inequalities, particularly in the United States,” writes the research team, which includes Stanford health economist Karen Eggleston, the director of the Asia Health Policy Program (AHPP) at APARC. Eggleston’s co-authors are Sungchul Park, an associate professor in Korea University’s Department of Health Policy and Management; Young Kyung Do, a professor in Seoul National University’s Department of Health Policy and Management and AHPP’s inaugural postdoctoral fellow; and David Cutler, the Otto Eckstein Professor of Applied Economics at Harvard University. 

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A Multidimensional View of Inequalities

To understand how income inequality plays out across the health systems of the two countries, the researchers examined how well these systems work for people at different income levels. Previous studies focused on a small number of health system performance indicators, and few have systematically compared countries. This new study does both.

The researchers used nationally representative data on 224,168 adults in the United States, surveyed between 2010-2019 and 2009-2018, and 179,452 adults in South Korea, surveyed between 2010-2019. They categorized these samples into income deciles based on annual household income in each country, which allowed them to track how outcomes vary from the lowest to the highest earners. Then they assessed 30 indicators across 6 distinct yet interconnected dimensions of health system performance: health care spending, health care utilization, access to care, health status, behavioral risk factors, and clinical outcomes.

The result is a comprehensive, cross-national portrait of the interplay between income inequalities and health system performance. “Investigating these domains collectively provides a multidimensional view of inequalities, highlighting areas where inequalities are most pronounced,” Eggleston and her collaborators write.

A Cross-Sectional Study of Two Contrasting Health Care Systems

South Korea's single-payer National Health Insurance offers universal health care coverage, but high out-of-pocket costs for services beyond the program still hinder equitable access. In the U.S. health system, by contrast, delivery of care is fragmented, market-driven, and marked by high out-of-pocket costs that worsen disparities for low-income groups.

But the study by Eggleston and her colleagues suggests that focusing only on national averages misses a critical question: that is, who benefits from the health system. It reveals that, across multiple dimensions of health system performance, inequalities are embedded in both the U.S. and Korean health systems despite their sharp differences, with the gaps particularly pronounced in the United States. The results show that:

• Adults in the United States had higher total health care spending than adults in South Korea, but, in both countries, higher-income adults had lower total health care spending than lower-income adults.
• In both countries, higher-income adults generally used fewer health care services than lower-income adults. Health care utilization was consistently lower in the US than in South Korea across all income levels.
• In both countries, higher-income adults had greater access to care than lower-income adults, but in South Korea, despite a higher number of doctor visits per capita, access to care was not better.
• Self-reported health status was similar between the two countries, but higher-income adults reported better health than lower-income adults in both countries.
• In both countries, behavioral risk factors such as overweight, smoking, and alcohol consumption were more common among lower-income adults, with income-related disparities more pronounced in the US.
• In both countries, clinical outcomes such as major depressive disorder, hypertension, and elevated cholesterol levels were also more common among lower-income adults, albeit these income-related disparities were generally modest in magnitude.
   

Embedded Inequalities

The study reveals inefficiency in the U.S. health system, which delivers clinical outcomes comparable to its Korean counterpart despite substantially higher per capita health care spending. The spending gap largely stems from higher prices, as utilization rates are similar in the two countries. These findings reinforce “the need for greater consideration of price regulation and measures to increase transparency,” write Eggleston and her colleagues.

Yet the United States had more favorable outcomes than South Korea on measures of access and care coordination, especially for lower-income populations, suggesting that certain components of the U.S. health care delivery system function effectively and that Korea’s achievement of comparable health outcomes at lower per-capita spending cannot be fully attributed to health system factors alone. Even under Korea’s universal health coverage, “unmet medical needs remain high, largely due to high out-of-pocket costs and limited benefit coverage.” 

Furthermore, the researchers’ analysis uncovered persistent patterns of income-based health inequalities across multiple domains in both countries, with disparities significantly wider in the United States. “Notably, income-related disparities in health care spending were largest in the lowest income decile, while spending remained relatively stable across higher deciles.”

While South Korea’s universal coverage appeared to narrow income-related disparities in health system performance, the research suggests that closing these gaps requires coordinated policy interventions, from health care financing and delivery reform to broader social and economic interventions that address the root causes of health inequalities.