Science is concerned with studying the world through observation and experiment. The data that emerge from science lead to knowledge about our physical and social world. That knowledge is, in and of itself, a worthwhile pursuit—it elevates us as humans, creates an understanding of the forces around us, and frees us from superstition and magical thinking. Some of the knowledge that comes from our scientific enterprise also leads directly to action, suggesting interventions that we can implement to improve the human condition.
Population health science is anchored in a universal human value—health—that is, itself, a foundational human condition that we wish to improve. As such, population health science is intimately linked with its operational arm—public health—and is more concerned with the pragmatic implications of its findings than may be other sciences, such as astrophysics. Yet population health science continues to embed, at its core, the universal concern of all science: understanding. Good population health science takes this role seriously, aspiring to inform our thinking, improving our knowledge. And that understanding does not have to be directly linked to actionable steps in the short term or point the way to experiment that can improve human health in the long term. Population health science fulfills its core function by generating the data that bear witness about the world around us, be it the natural world or the human-made world. Those in the science and practice of public health then need to ensure that the science is sufficiently consequential as to create a rich picture of the world that eventually can lend itself to action, toward the improvement of the health of the public.
BEARING WITNESS
Several articles in this issue of AJPH illustrate the role that population health science plays in bearing witness, in enriching our understanding of the world around us, even if they do not necessarily point to short-term action or solutions. Two articles about The Patient Protection and Affordable Care Act (ACA; Pub L No. 111-148, 124 Stat. 855 [March 2010]) Medicaid expansion start this discussion. First, an article by Himmelstein (p. 1243) used data from the Food Security Supplement to the Current Population Survey to compare trends in very low food security among low-income childless adults in states that did or did not expand Medicaid in 2014. They found that Medicaid expansion was associated with a 12.5% relative reduction in rates of very low food security, suggesting that the provision of health insurance has spillover effects, ameliorating aspects of poverty, beyond the core function of the insurance provisions of the ACA. In the second article about the ACA, Kobayashi et al. (p. 1236) used data from the Gallup-Sharecare Well-Being Index to assess whether changes occurred in access to health care, difficulty affording health care, and life satisfaction in states with and without Medicaid expansion. This study showed that although access to health care increased and difficulty affording health care decreased following the Medicaid expansion, no difference was seen in subjectively reported population well-being in states that had Medicaid expansion compared with those that did not have Medicaid expansion.
Both of these studies are consistent with a large body of work on the ACA and Medicaid expansion showing material improvement in health care access and related positive spillovers but also add a perspective on what ACA Medicaid expansion may not do. This is an enrichment of our understanding, a recognition of the importance of expanding health insurance access, but also, through careful bearing witness, points to dimensions of health that may be unaffected by health insurance. Neither of these studies, to our minds, points to clear actions, but they create the base for a public health of consequence that can build on this understanding as it aspires to create a healthier world.
ARTICULATING PROBLEMS WITHOUT SOLUTIONS
Two other articles in this issue of AJPH, tackling different topics, further illustrate how population health science improves understanding by bearing witness to the world. Siegler et al. (p. 1216) documented geographic areas with limited access to HIV preexposure prophylaxis (PrEP) providers. They used public data and a national database of PrEP providers to show that one in eight PrEP-eligible men who have sex with men lived more than a 30-minute drive from PrEP access and that, in particular, living in the South and nonurban areas was associated with increased odds of PrEP desert status. On a very different topic, Muldoon et al. (p. 1280) estimated population-level sexual assault prevalence in Ontario, Canada, between 2002 and 2016. They found that sexual assault was highest among females aged 15 to 19 years and 20 to 24 years and that, in particular, the sexual assault rate was increasing among those aged 15 years and older.
Both of these articles point to clear challenges to the health of populations. Better health can be built on us living in a world where measures that can prevent HIV are widely available to all and where sexual assault is not experienced by anyone. Yet neither of these articles points to easy solutions about how to tackle the problems documented here. That takes nothing away from the contribution that both articles make. Both articles represent population health science bearing witness to the world around, generating understanding that others can, should, and hopefully will use to implement efforts that can produce health.
CONNECTING THE DOTS
We conclude with an article in this issue of AJPH that takes the role of bearing witness one step further by asking how we can ensure even further that the science we document is translated and sets the path for action that can create a healthier world. We know that lifesaving organ transplantation is hampered by the availability of organs; this has been amply documented in the science and is widely discussed in the public press. Yet the challenge remains how to bridge that understanding into action and how to translate that message effectively to overcome this organ shortage.
Rodrigue et al. (p. 1273) carried out a cluster randomized trial to increase organ donor designation rates among adolescents by showing that testimonial video messaging and blended messaging were associated with higher donor designation rates than was informational messaging, even though the latter is the normative approach to promoting organ donor designation in the United States. This serves as an important reminder that the documentation of findings, the generation of science, left to its own devices may not lead to action. The work of translation lies in connecting the dots between population health science bearing witness and public health action that aims to generate a healthier world. Both represent aspects of a public health of consequence.
CONFLICTS OF INTEREST
The authors have no conflicts of interest to disclose.