Spatiotemporal variations in primary care physician density and population mortality across U.S. counties, 2005-2015

Sanjay Basu1,2*, Seth A. Berkowitz3, Russell S. Phillips2

1 Center for Primary Care and Outcomes Research and Center for Population Health Sciences, Departments of Medicine and of Health Research and Policy, Stanford University

2 Center for Primary Care, Harvard Medical School

3 Department of General Medicine and Clinical Epidemiology, University of North Carolina at Chapel Hill

*basus@stanford.edu

Background: Whether and to what degree primary care physicians can influence population-wide health outcomes remains heavily debated. Traditionally, assessments from the field of social epidemiology suggested that there is little or no measurable influence of medical care, including preventive and curative services delivered through primary care, on population health metrics such as life expectancy.1 Thomas McKweon’s 1976 assessment of death in England and Wales suggested that while life expectancy had increased by 23 years over the prior half century, little of the advance could be attributed to medical care;2 the previous year, Ivan Illich claimed more radically that medical care did more harm than good to population health.3 In the three decades that followed, improvements in life expectancy were more consistently attributed to advances in biomedicine including the treatment of hypertension,4,5 but contradictions also appeared, such as the increase in mortality rates from diseases amenable to medicine in areas with the most medical care resources.6

While many debates concerning medical care and population health focused on analysis of rich data from the United Kingdom, within the United States, debates during the early 21st century often compared aggregate U.S. medical care characteristics and population health statistics to that of international peers. Starfield and colleagues prominently argued that by comparing the United States to other countries with high average income, the availability of primary care services—that is, services provided by a generalist physician in an accessible manner across a broad range of illnesses and with longitudinal continuity between patient and provider—could be associated with lower all-cause and cause-specific mortality, when analyses were aggregated at the level of entire nations.7 State-level and metro-area assessments in the 1990’s also showed that large areas with more primary care physicians tended to have better birth outcomes and lower overall and cause-specific mortality,8–12 although whether these associations were independent of other types of medical care, overall healthcare infrastructure, and unaccounted-for community factors remains unclear.

Recent assessments of smaller area-level inequalities in the United States during the early 2000’s suggested increasing variations in life expectancy and cause-specific mortality across the nation, including stagnating or decreasing life expectancy in some counties, and increasing mortality from substance use and self-harm.13–15 Simultaneously, since the early 2000’s, healthcare reforms at the state and national level dramatically expanded financial support for primary care and increased the financial responsibility of medical care providers for population-health outcomes. For example, primary care providers and their associated healthcare ownership companies in many states have received increased funding to support proactive treatment of hypertension, diabetes, depression, substance abuse, and other chronic conditions, and conversely received financial penalties if they failed to meet population health metrics for their catchment population.16–21 Large state and national initiatives are now expanding support for population health measures to be integrated into primary care clinics, such as by coordinating services for income, food, employment, and housing support through primary care clinics, and directing an increasing supply of primary care physicians to underserved regions through financial incentives.22–24

How primary care physician supply has changed over the last decade in the United States remains unclear. It also remains unclear to what extent changes in primary care physician supply can help to explain recent temporal and geographic variations in mortality across the United States. Addressing these uncertainties is critical to identify whether existing primary care initiatives are related to population health, and whether further efforts to expand primary care physician supply have the potential to produce measurable population health improvements. Here, we sought to assess temporal and geospatial variations in primary care physician density, and test the a priori null hypothesis that those variations do not significantly relate to variations in life expectancy and cause-specific mortality among U.S. counties from 2005 through 2015.

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