G. Richard, MD, MSPH Naazneen Pal, MPH Eduardo C. Gonzalez, MD Jeanne M. Ferrante, MD Daniel J. Van Durme, MD John Z. Ayanian, MD, MPP Jeffrey P. Krischer, PhD Tampa, Florida, and Boston, Massachusetts Submitted, revised, July 21, 1999. From the Department of Family Medicine (R.G.R., N.P, E.C.G., J.M.F., D.J.V) and the H. Lee Moffitt Cancer Center and Research Institute (R.G.R., J.P.K), University of South Florida, Tampa, and the Division of General Medicine, Department of Medicine, Brigham & Women’s Hospital and the Department of Health Care Policy, Harvard Medical School (J.Z.A.). Reprint requests should be addressed to Richard Roetzheim, MD, MSPH, Department of Family Medicine, University of South Florida, 12901 Bruce B. Downs Blvd, MDC 13, Tampa, FL 33612.
References
Table 3 shows the effects of primary care and specialty physician supplies when analyses were stratified by characteristics of the patient’s residence. In urban and high socioeconomic areas, an increasing supply of primary care physicians was associated with earlier diagnosis of colorectal cancer, while an increasing supply of specialty physicians was associated with greater odds of late-stage diagnosis. In nonurban areas there was a trend toward earlier stage at diagnosis with increasing supply of primary care physicians that did not reach statistical significance.
Comparing primary care physician specialty supplies at the local level, an increasing supply of general internists was found to be associated with decreased odds of late-stage diagnosis (c2 for linear trend = 7.54, P = .006). For each 10-percentile increase in the supply of general internists the odds of late-stage diagnosis decreased 3% (adjusted OR = 0.97; 95% CI, 0.95 - 0.99). In contrast, an increasing supply of obstetrician/gynecologists at the local level was associated with greater odds of late-stage diagnosis (c2 for linear trend = 9.52; P = .002). Each 10-percentile increase in the supply of obstetrician/gynecologists was associated with a 4% increase in the odds of late-stage diagnosis (adjusted OR = 1.04; 95% CI, 1.01 - 1.06). There was no significant association between the supply of family/general practice physicians at the local level and the odds of late-stage diagnosis (c2 for linear trend = 2.83, P = .09).
Because obstetrician/gynecologists only serve as primary care providers for women, we repeated analysis stratified by sex Table 4. There was no statistical association between primary care physician specialty supplies and odds of late-stage diagnosis for men. Among women, however, increasing supplies of family/general practitioners and general internists were associated with lower odds of late-stage diagnosis, while an increasing supply of obstetrician/gynecologists was associated with greater odds of late-stage diagnosis.
We also examined whether the odds of late-stage diagnosis might be affected by the supply of gastroenterologists. The supply of gastroenterologists was not associated with stage at diagnosis when measured at either the county level (adjusted OR = 1.007; 95% CI, 0.98 - 1.03; P = .55) or at the local level (adjusted OR = 1.007; 95% CI, 0.998 - 1.02; P = .14).
Results were similar when logistic models were repeated with cases restricted to invasive cancers only, to patients having fee-for-service insurance only, or when cases were restricted to ages for which colorectal screening is most commonly recommended (50 years and older).22,60,61 Results also did not differ when physician supply was measured relative to other ZIP code cluster sizes (3, 7, and 10 ZIP codes).
We reestimated model parameters and errors using the method of generalized estimating equations to control for any effects of clustering within the data. Results were similar. The effects of regional primary care and specialty care supplies, for example, were unchanged when potential clustering of data was taken into account (primary care physician supply OR = 0.95; 95% CI, 0.91 - 0.99; P = .01; specialty care physician supply OR = 1.05; 95% CI, 1.01 - 1.09; P = .007).
Discussion
The supplies of primary care and specialty physicians were significantly associated with stage at diagnosis for patients with colorectal cancer. As the supply of primary care physicians increased, the odds of late-stage diagnosis decreased. Unexpectedly, an increasing supply of specialist physicians was found to be associated with later stage at diagnosis. We found no relationship, however, between overall physician supply and stage at diagnosis.
If the associations we observed were causal, it would imply that physician supply had a fairly substantial impact on the likelihood of early colorectal cancer diagnosis. The odds ratio contrasting the highest primary care physician supply with the lowest was 1.60, which is similar in magnitude to the odds ratio we have previously reported (OR = 1.67) describing the effects of being uninsured.62 On the basis of the odds ratios we observed in this study, we concluded that 437 (8%) of the 5463 patients diagnosed with late-stage colorectal cancer in Florida could theoretically have been diagnosed at an earlier stage if all patients resided either in counties having a primary care physician supply of the highest decile or in counties having a specialty physician supply of the lowest decile. If both conditions were true, 874 of the 5463 (16%) patients diagnosed with late-stage cancer could theoretically have been diagnosed earlier.
Although it is easy to envision how an adequate supply of primary care physicians might contribute to earlier detection of colorectal cancer, it is less clear why an increasing supply of specialists would be detrimental. One possibility is that primary care physicians provide early cancer detection services that specialists do not, and that they compete to provide for patients’ health care needs. If patients are more likely to have their health care needs met by specialists when there is an abundant supply, this may result in decreased exposure to early detection services supplied by primary care physicians.
