More may be better: evidence of a negative relationship between physician supply and hospitalization for ambulatory care sensitive conditions.

OBJECTIVE To conduct an empirical test of the relationship between physician supply and hospitalization for ambulatory care sensitive conditions (ACSH). DATA SOURCES/STUDY SETTING A data set of county ACSH rates compiled by the Safety Net Monitoring Initiative of the Agency for Healthcare Research and Quality (AHRQ). The analytical data set consists of 642 urban counties and 306 rural counties. We supplemented the AHRQ data with data from the Area Resource File and the Environmental Protection Agency. STUDY DESIGN Ordinary least squares regression estimated ACSH predictors. Physician supply, the independent variable of interest in this analysis, was measured as a continuous variable (MDs/100,000). Urban and rural areas were modeled separately. Separate models were estimated for ages 0-17, 18-39, and 40-64. DATA EXTRACTION METHODS Data were limited to 20 states having more than 50 percent of counties with nonmissing data. PRINCIPAL FINDINGS In the urban models for ages 0-17, standardized estimates indicate that, among the measured covariates in our model, physician supply has the largest negative adjusted relationship with ACSH (p<.0001). For ages 18-39 and 40-64, physician supply has the second largest negative adjusted relationship with ACSH (p<.0001, both age groups). Physician supply was not associated with ACSH in rural areas. CONCLUSIONS Physician supply is positively associated with the overall performance of the primary health care system in a large sample of urban counties of the United States.