The effects of physician supply on the early detection of colorectal cancer

BACKGROUND. Policymakers question whether there is a relationship between the number and distribution of physicians and the outcomes for important health conditions. We hypothesized that increasing primary care physician supply would be related to earlier detection of colorectal cancer. METHODS. We identified incident cases of colorectal cancer occurring in Florida in 1994 (n = 8933) from the state cancer registry. We then obtained measures of physician supply from the 1994 American Medical Association Physician Masterfile and examined the effects of physician supply (at the levels of county and ZIP code clusters) on the odds of late-stage diagnosis using multiple logistic regression. RESULTS. For each 10-percentile increase in primary care physician supply at the county level, the odds of late-stage diagnosis decreased by 5% (adjusted odds ratio [OR] = 0.95; 95% confidence interval [Cl], 0.92 - 0.99; P = .007). For each 10-percentile increase in specialty physician supply, the odds of late-stage diagnosis increased by 5% (adjusted OR = 1.05; 95% Cl, 1.02 - 1.09; P = .006). Within ZIP code clusters, each 10-percentile increase in the supply of general internists was associated with a 3% decrease in the odds of late-stage diagnosis (OR = 0.97; 95% Cl, 0.95 - 0.99; P = .006), and among women, each 10-percentile increase in the supply of obstetrician/gynecologists was associated with a 5% increase in the odds of late-stage diagnosis (OR = 1.05; 95% Cl, 1.01 - 1.08; P = .005). CONCLUSIONS. If the relationships observed were causal, then as many as 874 of the 5463 (16%) late-stage colorectal cancer diagnoses are attributable to the physician specialty supply found in Florida. These findings suggest that an appropriate balance of primary care and specialty physicians may be important in achieving optimal health outcomes.