Recent health care reforms in the United States encourage improved population health outcomes and primary care functions, but most prior studies of the value of primary care have relied on cross sectional studies that demonstrate associations with desired outcomes, but cannot provide evidence of causation. In a study in JAMA Internal Medicine, a paper led by assistant professor of medicine at Stanford Medical School Sanjay Basu, MD, PhD that also included assistant professor of medicine and health care policy Asaf Bitton, MD, MPH, professor of health care policy Bruce E. Landon, MD, MBA, and Director of Center for Primary Care and William Applebaum Professor of Medicine at Harvard Medical School Russell S. Phillips, MD, investigated if increasing the supply of primary care physicians can improve population health outside of other health care and socioeconomic factors. This paper is important because it examines whether changes in primary care supply within an area are causally related to changes in population level life expectancy.

The study team examined the association between primary care physician supply changes and population life expectancy from 2005-2015 using data from multiple different sources. Due to disproportionate rural losses and general population size increases at a county level, the mean (SD) density of primary care physicians relative to population size decreased from 46.6 per 100 000 population to 41.4 per 100 000 population (95% CI, 0.0-108.6 per 100 000 population), with greater losses in rural areas The study found that communities that added ten primary care physicians per 100,000 citizens (a one standard deviation increase) saw a 51.5-day increase in patient’s life expectancy. Cardiovascular, cancer, and respiratory related mortality were all reduced in areas that saw this growth, but mortality causes that would be unrelated to primary care physician supply (such as accidents) were unaffected.

The study suggests that increasing primary care physician supply can reduce mortality and have a positive effect on population health.