According to a study published in JAMA Internal Medicine, a greater number of primary care physicians per capita was associated with improved life expectancy, suggesting that physician supply has an important effect on population health.

The investigators of this observational study sought to identify changes in primary care physician supply at the local level and to examine associations between population-level physician supply and mortality across US counties between 2005 and 2015.

The study investigators obtained population counts from the US Census Bureau and data on primary care physician counts from the American Medical Association Physician Masterfile for the years 2005, 2010, and 2015. The primary and secondary outcomes of age-adjusted life expectancy and cause-specific mortality, respectively, were estimated using US population and individual-level claims data for the years 2005, 2010, and 2014. For the present study, cause of death was divided into 5 major categories: cardiovascular disease, cancer, infectious diseases, respiratory tract diseases, and substance use or injury. In analyzing the association between physician supply and population-level mortality, adjustments were made for potential confounders relating to health care, demographic and socioeconomic factors, and patient behaviors.

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Between 2005 and 2015, the primary care physician supply increased from 196,014 to 204,419 physicians; however, the mean density of primary care physicians relative to population size decreased from 46.6 per 100,000 population (95% CI, 0.0-114.6) to 41.4 per 100,000 population (95% CI, 0.0-108.6). The investigators suggest these patterns reflect a disproportionately greater loss of physician supply in rural areas and an increase in the general population count. The number of specialist physicians increased from 699,989 to 805,277 from 2005 to 2015, but this change was only minimally associated with changes in primary physician supply.

In adjusted analyses, every 10 additional primary care physicians per 100,000 population corresponded to a 51.5-day life-expectancy increase (95% CI, 29.5-73.5); similarly, an increase of 10 additional specialist physicians per 100,000 population was associated with a life-expectancy increase of 19.2 days (95% CI, 7.0-31.3). Adjusting for covariates, an increase of 10 additional primary care physicians per 100,000 population was associated with reductions in cardiovascular mortality by 30.4 deaths per million (95% CI, -52.4 to -8.4); cancer mortality by 23.6 deaths per million (95% CI, -35 to -12.3); and respiratory mortality by 8.8 deaths per million (95% CI, -15.3 to -2.2). The investigators found similar results when performing instrumental variable regressions and individual-level analyses.

A limitation of the study was the ecological nature used to analyze relationships between population-level data. In addition, to avoid the ecological fallacy, private insurance data was used for individual-level associations. The inability to randomize participants to receive care from areas of varied physician supply may allow for additional confounding.

Change in primary care physician supply patterns across the US shows an increase in the total number of physicians even with disproportionate losses identified in rural areas. Greater primary care physician density was associated with lower population mortality and the investigators suggest that physician supply importantly affects population health.


Basu S, Berkowitz SA, Phillips RL, Bitton A, Landon BE, Phillips RS. Association of primary care physician supply with population mortality in the United States, 2005-2015 [published online February 18, 2019]. JAMA Intern Med. doi:10.1001/jamainternmed.2018.7624