Letting Perfect be the Enemy of Good?

This is a guest post by J. Michael McWilliams, MD, PhD, assistant professor of health care policy and of medicine at Harvard Medical School and an associate physician in the Division of General Medicine at Brigham and Women’s Hospital. He is also author of the 2009 Milbank Quarterly paper “Health Consequences of Uninsurance among Adults in the United States: Recent Evidence and Implications.” (This post has been cited in the 18 February 2010 edition of Health Wonk Review.)

An Atlantic Monthly article by Megan McArdle questions whether health insurance coverage saves lives, drawing from a narrow slice of the literature to suggest the beneficial effects of insurance coverage on mortality might be negligible.  While it is true these effects have been challenging for researchers to assess accurately, this question deserves more than a selective reading of the literature to inform the public and policymakers properly.  Indeed, when reviewed comprehensively and with an understanding of key clinical and methodological nuances, the research to date provides consistent and compelling evidence that health insurance coverage significantly improves health outcomes, particularly for adults with treatable conditions (McWilliams 2009).

Studies on the health consequences of uninsurance can be broadly categorized as observational or quasi-experimental.  Observational studies compare health outcomes between insured and uninsured adults and use statistical techniques to control for differences in other predictors of health between the two groups.  These studies are fundamentally limited because it is usually impossible to control for all possible differences and some differences may be both causes and consequences of insurance coverage.  Consequently, observational results may underestimate or overestimate the true effects of coverage.  From the sizable observational literature, McArdle selects just one negative study to suggest insurance coverage may not affect mortality (Kronick 2009).  Yet several other observational studies that controlled for an equally robust set of characteristics have consistently demonstrated a 35-43% greater risk of death within 8-10 years for adults who were uninsured at baseline and even higher relative risks for older uninsured adults with treatable chronic conditions such as diabetes and hypertension (Baker et al. 2006; McWilliams et al. 2004; Wilper et al. 2009).

Because these observational studies are not sufficiently rigorous to support causal conclusions, we should look to studies that are more experimental in design for more definitive evidence.  McArdle cites a principal finding of the RAND Health Insurance Experiment (HIE) that more generous coverage led to more health-care utilization but not better health outcomes on average.  However, the set of findings from the RAND HIE that is arguably more salient to this discussion is that more generous coverage did lead to better blood pressure control and lower predicted mortality for low-income adults with hypertension — adults that resemble the uninsured population more closely than the average adult.  Moreover, the RAND study was conducted in the 1970s, prior to numerous advances that have improved the effectiveness of medical care for many acute and chronic conditions.

From the quasi-experimental literature, McArdle cites evidence of a lack of immediate survival gains with near-universal Medicare coverage after age 65 in the general population (Card et al. 2004; Levy, and Meltzer 2008).  From a clinical perspective, however, we should not expect immediate survival gains for most previously uninsured adults because mortality is such a distal outcome.  Survival gains may not manifest for years after improved chronic disease control and cancer screening are established, suggesting much more complex improvements in mortality trends are likely to evolve after age 65 in response to universal coverage.  Quasi-experiments that rely on abrupt discontinuities occurring with age are not well suited to capturing these complex but potentially large effects.  Consequently, the absence of evidence suggested by these studies is not evidence of absence.  In contrast to the general population, immediate mortality effects might be expected for acutely ill patients for whom coverage may improve access to life-saving procedures and therapies.  Indeed, a more recent study found age-eligibility for Medicare was associated with a substantial and lasting reduction in mortality for patients who were hospitalized for a range of acute illnesses that were amenable to treatment (Card et al. 2009).

Because many quasi-experimental strategies are geared to capture effects of insurance coverage only if they occur in the short term, they are better suited to examining proximal or intermediate health outcomes.  Therefore, perhaps more can be learned about the effects of insurance coverage on mortality from studies that rigorously examine effects on health outcomes that are highly predictive of mortality.  To date, numerous studies have found consistently beneficial and often significant effects of insurance coverage on health across a comprehensive set of outcomes and a broad range of treatable chronic and acute conditions that affect many adults in the U.S., including hypertension, coronary artery disease, congestive heart failure, stroke, diabetes, HIV infection, depressive symptoms, acute myocardial infarction, acute respiratory illnesses, and traumatic injuries (McWilliams 2009).  In particular, several studies have robustly demonstrated positive effects of near-universal Medicare coverage after age 65 on self-reported health outcomes and clinical measures of disease control, particular for adults with cardiovascular disease or diabetes who make up two-thirds of the near-elderly (Decker and Remler 2004; McWilliams et al. 2007, 2009).  Thus, when rigorous study designs have been coupled with appropriate outcomes and applied to clinical populations for whom medical care is effective, the evidence that insurance coverage improves health and survival is consistent and convincing.

How many lives would universal coverage save each year?  A rigorous body of research tells us the answer is many, probably thousands if not tens of thousands.  Short of the perfect study, however, we will never know the exact number.  In the meantime, we can let perfect be the enemy of good.  Or we can recognize the evidence to date is sufficiently robust for policymakers to proceed confidently with health care reforms that promise substantial health and financial benefits for millions of uninsured Americans.


Baker, D. W., J. J. Sudano, R. Durazo-Arvizu, J. Feinglass, W. P. Witt, and J. Thompson. 2006. “Health insurance coverage and the risk of decline in overall health and death among the near elderly, 1992-2002.” Med Care 44:277-82.

Card, D., C. Dobkin, and N. Maestas. 2004. “The impact of nearly universal insurance coverage on health care utilization and health: evidence from Medicare”. NBER Working Paper Series. Cambridge, MA: National Bureau of Economic Research.

Card, D., C. Dobkin, and N. Maestas. 2009. “Does Medicare save lives?” Quart J Econ 124(2):531-96.

Decker, S. L. and D. K. Remler. 2004. “How much might universal health insurance reduce socioeconomic disparities in health? : A comparison of the US and Canada.” Appl Health Econ Health Policy 3:205-16.

Kronick, R. 2009. “Health insurance coverage and mortality revisited.” Health Serv Res 44:1211-31.

Levy, H. and D. Meltzer. 2008. “The impact of health insurance on health.” Annu Rev Public Health 29:399-409.

McWilliams, J. M. 2009. “Health consequences of uninsurance among adults in the United States: recent evidence and implications.” Milbank Q 87:443-94.

McWilliams, J. M., E. Meara, A. M. Zaslavsky, and J. Z. Ayanian. 2007. “Health of previously uninsured adults after acquiring Medicare coverage.” JAMA 298:2886-94.

McWilliams, J. M., E. Meara, A. M. Zaslavsky, and J. Z. Ayanian. 2009. “Differences in control of cardiovascular disease and diabetes by race, ethnicity, and education: U.S. trends from 1999 to 2006 and effects of Medicare coverage.” Ann Intern Med 150:505-15.

McWilliams, J. M., A. M. Zaslavsky, E. Meara, and J. Z. Ayanian. 2004. “Health insurance coverage and mortality among the near-elderly.” Health Aff (Millwood) 23:223-33.

Wilper, A. P., S. Woolhandler, K. E. Lasser, D. McCormick, D. H. Bor, and D. U. Himmelstein. 2009. “Health insurance and mortality in US adults.” Am J Public Health 99(12):2289-95.

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