Medicare patients living in areas with higher levels of practicing primary care physicians have lower death rates and make fewer trips to the hospital for preventable conditions, according to a study by Dartmouth Atlas Project investigators published in the Journal of the American Medical Association.

In the JAMA study, researchers sought to determine the association between the adult primary care physician workforce—that is, the number of physicians available for a given population in an area—and individual Medicare patient outcomes. The findings suggest that a larger local workforce of primary care physicians has a positive benefit for Medicare patients, but this association may not simply be the result of having more physicians in an area who are trained in primary care. Instead, the benefits of the primary care workforce may be more from the amount of ambulatory clinical care provided, rather than the number of primary care physicians locally available.

Medicare patients living in areas with a higher level of adult primary care physicians per population had modestly lower mortality and fewer hospitalizations for what are known as ambulatory care-sensitive condition hospitalizations. ACSC hospitalizations are regarded as largely preventable with proper primary or other outpatient care. However, the associations were much stronger with a measure of an area's primary care activity that was based on the amount of care delivered in an office or clinic setting by primary care physicians. The difference is important because not all doctors trained in primary care work in ambulatory settings. Some work in emergency departments or as hospitalists.

Medicare patients living in areas with the highest amount of primary care delivered by physicians trained in primary care had 5 percent lower mortality, 9 percent fewer ACSC hospitalizations and 1 percent higher total Medicare program spending. Previous studies have used the AMA Masterfile, the most widely used physician workforce data source, to measure the physician workforce. However, this study's results suggest that the AMA Masterfile may not accurately reflect the proportion of primary care-trained physicians actually providing ambulatory primary care. This is because physicians may be counted as primary care according to their self-designated specialty on the AMA Masterfile, but not practice in an ambulatory setting.

To address this in the study, researchers introduced a new measure of the primary care workforce derived from Medicare claims to test hypotheses that high levels of primary care physicians are associated with lower mortality, fewer ACSC hospitalizations and lower spending. Researchers differentiated areas where physicians are providing ambulatory primary care in an office setting from areas with higher numbers of physicians who trained in primary care, according to Medicare office- and clinic-based claims, but are not practicing physicians.