An interesting new study of the 2006 Massachusetts health reform law adds to a growing body of evidence demonstrating that coverage expansions and related reforms help to improve overall health status. Specifically, this is the first study of the Massachusetts reform to suggest that its health effects are sufficiently large so as to be detectable at the population level, as reflected in the overall mortality rates for counties. These very encouraging results beg the question of how the results were achieved — which components of comprehensive reform are responsible for the drop in mortality?

The estimated 2.9% reduction in all-cause mortality represents a large and significant drop in deaths at the population level, particularly given the relatively short 5-year study period following health reform implementation. Chronic diseases are the main drivers of morbidity and mortality in the U.S., and most of these diseases chip away at our health over long periods of time, eventually causing death. Interventions that can make a dent in overall death rates in the space of just a few years are few and far between, and certainly worthy of attention (as I noted in a related commentary on this study).

The study authors focus on the expansion of health insurance coverage as the active ingredient in the Massachusetts law that is likely responsible for the drop in deaths. The results imply that for every 830 adults who gained insurance coverage, 1 death was prevented. However, I am not entirely convinced of this implication, and believe there could be more to the story of how Massachusetts lowered their mortality rates.

This study examines the population-level health effects of a health reform strategy that included not only insurance coverage expansions but also improvements in preventive services delivery and public health protections. Other elements of Massachusetts’ health reform strategy, such as reducing out-of-pocket costs for clinical preventive services and enhancing public health programs and infrastructure, may have contributed to the drop in mortality. For example, other studies have found large reductions in smoking prevalence and tobacco-associated health events among Massachusetts Medicaid recipients after the state added a comprehensive tobacco cessation benefit to its Medicaid program in 2006 as part of its health reform strategy. These preventive strategies and the resulting drop in tobacco exposure could plausibly explain some of the observed drop in mortality.

Importantly, the research design employed in this study cannot definitively attribute the mortality reductions to the gains in insurance coverage. The study uses county-level mortality data, so we cannot be sure that the people who gained coverage are the ones who experienced a reduction in their mortality risk (the classic ecological fallacy problem). The study hinges on comparing Massachusetts’ 14 counties to a statistically matched comparison group of counties outside the state, so with such a small number of intervention counties there is always the risk of systematic nonequivalence between the intervention and comparison counties—particularly when some of the covariates used for matching (like the baseline uninsured rate) are themselves subject to considerable sampling error.

Of course, other studies that have focused more narrowly on coverage expansions – such as the recent Oregon Medicaid experiment studies – have failed to find evidence of significant mortality reductions. Most of these studies use person-level rather than county-level analyses, so they are not able to detect population-level effects and they are not vulnerable to ecological fallacy. And the Oregon studies so far have been limited to shorter follow-up periods than the five years used in this latest Massachusetts study. Still, the mixed results from existing studies raise the possibility that insurance coverage by itself may not be sufficient to achieve large population-level health improvements. The mortality reductions found in Massachusetts may be attributable to the study’s population-level perspective, which captures the effects not only of insurance coverage expansion but also of other elements of reform. If so, combining coverage expansion with enhanced prevention and public health programming might just be the secret recipe for successful health reform.

These results provide encouraging news about the population-level health gains that ACA may produce. Before their 2006 reform, Massachusetts was already better off than most other U.S. states in terms of health insurance coverage and overall health status. Consequently, we might expect to see even larger health gains as similar reforms take hold in less-advantaged states. Of course, some of these less-advantaged states have chosen not to implement some of the ACA’s reforms to date – specifically the Medicaid coverage expansions. And the ACA’s prevention and public health programming has been scaled back considerably as a result of sequestration and decisions to use Prevention and Public Health Fund resources for other priorities. So, ACA’s population-level health effects remain uncertain and a very important target for ongoing study.