Primary Care Physician Supply and Colorectal Cancer

Although there is continued interest in the composition of the United States physician work force,^18-25 there have been surprisingly few studies demonstrating the effects of physician supply on health-related outcomes. Some studies have suggested that an oversupply of specialists may contribute to higher health care costs.^22,26-28 Primary care physician supply has been correlated with reduced hospitalization rates for ambulatory care–sensitive conditions^29,30 and with improved access and overall use of ambulatory health services.^31-34

We have previously shown associations between primary care physician supply and earlier detection of breast cancer, colorectal cancer, and malignant melanoma.^16,35,36 These findings are consistent with studies showing that patients who have a family physician are more likely to receive a diagnosis of early-stage cancer.³⁷ Our study suggests that increasing supplies of primary care physicians might also be associated with reduced incidence and mortality for some cancers. In contrast, increased overall supplies of physicians have not been associated with improved cancer outcomes, suggesting that a balanced physician work force may be necessary to achieve optimal health outcomes.

Physician specialty choice and practice location are driven by many factors, including the location of training programs at medical schools and residencies, role models in medical school, education debt, lifestyle, and other issues. These factors influence the types of physicians that practice in various locations, and as a result may influence the health care of the population in that area. As the physician work force is studied and policy decisions are made, it will be important to consider measurable health care outcomes in addition to projected demands based on economic forces.³⁸

Limitations

This study has a number of important limitations that should be considered. First, ecologic studies are subject to the ecologic fallacy, in which associations at the population level do not accurately reflect associations at the individual level. We did not have information on individual patients’ actual use of physician services, for example, so patients’ actual access to primary care may have been different than that predicted by county-level measures. Ecologic studies have very limited ability to establish causation, and follow-up studies conducted at the individual patient level (such as case-control or cohort studies) will be necessary to confirm these findings. The exploratory nature of selecting variables for ecologic studies may also increase type 1 statistical errors, falsely concluding that associations exist when they have actually occurred by chance.

We did not have information on other colorectal cancer risk factors, such as dietary patterns, rates of family history, or rates of ulcerative colitis. We also lacked information on rates of detection of precancerous polyps, and the age/sex distribution of physicians, which would have strengthened our study. Because incidence and mortality rates were established according to the patient’s county of residence rather than the location of diagnosis or treatment, we do not believe the associations observed were the result of referral patterns (eg, patients with suspected late-stage disease being referred to areas with higher-specialty physician supply). However, physician supply might be correlated with other unmeasured characteristics of our health care delivery system, which could account for the observed associations. Finally, our study was restricted to colorectal cancer in Florida, which may not be representative of other diseases or other parts of the country.

Conclusions

Both the incidence and mortality of colorectal cancer were decreased in Florida counties that had a greater supply of primary care physicians. Overall physician supply, however, was unrelated to colorectal cancer mortality or incidence. These associations will need to be confirmed with studies conducted at the individual level.