The road to efficiency? Re-examining the impact of the primary care physician workforce on health care utilization rates

Research suggests that primary care physicians may help to control health care costs by encouraging more efficient service use. However, most studies do not account for data aggregation effects that can significantly affect the direction and magnitude of findings. To re-examine the association between the proportion of primary care physicians and health care utilization rates in an area, and investigate the potential impact of aggregating data to different geographic levels on these observed associations, we estimate four distinct cross-sectional multivariate regression models to predict health care utilization at the county level and the metropolitan statistical area (MSA) level using data from 2007. Our study focuses on health care utilization in the United States using inpatient admissions, outpatient visits, emergency room visits, and total (both inpatient and outpatient) surgeries as dependent variables in separate regressions. The key independent variable is the proportion of primary care physicians in the area. Several community-level control variables are also included. We find that a higher proportion of primary care physicians in the area's physician supply is associated with a decreased number of inpatient admissions at the MSA level, but not the county level, and a decreased number of emergency room visits at the county level, but not the MSA level. Outpatient visits and total surgeries are not associated with the proportion of primary care physicians. From our findings we are able to conclude that there is some evidence that a higher concentration of primary care physicians is associated with a decrease in health care utilization, but these findings depend on the level of aggregation. Investigators should be aware of the implications of aggregating data and acknowledge any resultant limitations.