Abstract
About 28 million Americans are currently uninsured, and millions more could lose coverage under policy reforms proposed in Congress. At the same time, a growing number of policy leaders have called for going beyond the Affordable Care Act to a single-payer national health insurance system that would cover every American. These policy debates lend particular salience to studies evaluating the health effects of insurance coverage. In 2002, an Institute of Medicine review concluded that lack of insurance increases mortality, but several relevant studies have appeared since that time. This article summarizes current evidence concerning the relationship of insurance and mortality. The evidence strengthens confidence in the Institute of Medicine's conclusion that health insurance saves lives: The odds of dying among the insured relative to the uninsured is 0.71 to 0.97.
In several specific conditions, the uninsured have worse survival, and the lack of coverage is associated with lower use of recommended preventive services.
The Oregon Health Insurance Experiment, the only available randomized, controlled trial that has assessed the health effects of insurance, suggests that insurance may cause a clinically important decrease in mortality, but wide CIs preclude firm conclusions.
The 2 National Health and Nutrition Examination Study analyses that include physicians' assessments of baseline health show substantial mortality improvements associated with coverage. A cohort study that used only self-reported baseline health measures for risk adjustment found a nonsignificant coverage effect.
Most, but not all, analyses of data from the longitudinal Health and Retirement Study have found that coverage in the near-elderly slowed health decline and decreased mortality.
Two difference-in-difference studies in the United States and 1 in Canada compared mortality trends in matched locations with and without coverage expansions. All 3 found large reductions in mortality associated with increased coverage.
A mounting body of evidence indicates that lack of health insurance decreases survival, and it seems unlikely that definitive randomized, controlled trials can be done. Hence, policy debate must rely on the best evidence from observational and quasi-experimental studies.
The IOM committee also reviewed evidence on the effects of health insurance in specific circumstances and medical conditions. It concluded that uninsured patients, even when acutely ill or seriously injured, cannot always obtain needed care and that coverage improves the uptake of essential preventive services and chronic disease management. The report found that uninsured patients with cancer presented with more advanced disease and experienced worse outcomes, including mortality; that uninsured patients with diabetes, cardiovascular disease, end-stage renal disease, HIV infection, and mental illness (the five other conditions reviewed in depth) had worse outcomes than did insured patients; and that uninsured inpatients received less and worse-quality care and had higher mortality both during their hospital stays and after discharge.
Table 1. Summary of Studies on Relationship Between Insurance Coverage and All-Cause Mortality*
We searched PubMed and Google Scholar on May 19, 2017, for English-language articles by using the following terms: [(uninsured) or (health insurance) or (uninsurance) or (insurance)] and [(mortality) or (life expectancy) or (death rates)]. After identifying relevant articles, we searched their bibliographies and used Google Scholar's cited by feature to identify additional relevant articles. We limited our scope to articles reporting data on the United States, quasi-experimental studies of insurance expansions in other wealthy nations, and recent cross-national studies. We contacted the authors of 4 studies to clarify their published reports on mortality outcomes.
We excluded most observational studies that compared uninsured persons with those insured by Medicaid, Medicare, or the Department of Veterans Affairs because preexisting disability or illness can make an individual eligible for these programs. Hence, relative to those who are uninsured, publicly insured Americans have, on average, worse baseline health, thereby confounding comparisons. Conversely, comparisons of the uninsured to persons with private insurance (which is often obtained through employment) may be confounded by a healthy worker effect: that is, that persons may lose coverage because they are ill and cannot maintain employment. Nonetheless, most analysts of the relationship between uninsurance and mortality have viewed the privately insured as the best available comparator, with statistical controls for employment, income, health status, and other potential confounders.
In sum, the OHIE yields a (nonsignificant) point estimate that Medicaid coverage reduced mortality by 0.13 percentage points, equivalent to a (nonsignificant) odds ratio of 0.84.
Several routinely collected federal surveys that include information about health insurance coverage have been linked to the National Death Index, allowing researchers to compare the mortality rates over several years of respondents with and without coverage at the time of the initial survey. One weakness of these studies is their lack of information about the subsequent acquisition or loss of coverage, which many people cycle into and out of over time. This dilutes coverage differences and may lead to underestimation of the effects of insurance coverage.
Two studies have analyzed the effect of uninsurance on mortality using data from the National Health and Nutrition Examination Survey (NHANES), which obtains data from physical examination and laboratory tests among participants.
Several researchers have used data from the Health and Retirement Study (HRS)a longitudinal study that has followed cohorts enrolled at age 51 years or olderto assess the effect of insurance coverage on mortality. The HRS periodically surveys respondents and their families and has been linked to Medicare and National Death Index data.
The evidence accumulated since the publication of the IOM's report in 2002 supports and strengthens its conclusion that health insurance reduces mortality. Several newer observational and quasi-experimental studies have found that uninsurance shortens survival, and a few with null results used confounded or questionable adjustments for baseline health. The results of the only recent RCT, although far from definitive, are consistent with the positive findings from cohort and quasi-experimental analyses.
Table 2. Why the Causal Relationship of Health Insurance to Mortality Is Hard to Study
Finally, our focus on mortality should not obscure other well-established benefits of health insurance: improved self-rated health, financial protection, and reduced likelihood of depression. Insurance is the gateway to medical care, whose aim is not just saving lives but also relieving human suffering.
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