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Cancer. Author manuscript; available in PMC 2010 July 23.
Published in final edited form as:
PMCID: PMC2909270

Associations of Physician Supplies With Breast Cancer Stage at Diagnosis and Survival in Ontario, 1988 to 2006



The authors examined whether the supply of primary care physicians had protective effects on breast cancer stage and survival in Ontario and whether supply losses during the 1990s were associated with diminished protection.


Random samples of the Ontario Cancer Registry, respectively, provided 879 women and 951 women who were diagnosed with breast cancer between 1988 and 1990 (followed until 1996) and 1998 and 2000 (followed until 2006), respectively. Active physician supply data (1991 and 2001) joined to each woman’s census division of residence was taken from the Scott’s Medical Database.


Protective thresholds were observed among the earlier cohort for supplies of general practitioners (7 per 10,000 population) and supplies of obstetricians/gynecologists (6 per 100,000 population) at or above which women with breast cancer were significantly more likely to have been diagnosed with localized disease and to have survived for ≥5 years. These protective effects seemed generally attenuated among the more recent cohort. The risk of living in primary care physician-undersupplied areas increased significantly between 1991 and 2001 (10%–30%), and such physician supply losses were associated with reduced cancer care protection, including less prevalent early diagnoses (odds ratio [OR], 1.60; 95% confidence interval [95% CI], 1.00–2.58) and lower 5-year survival rates (OR, 1.62; 95% CI, 1.03–2.55).


Primary care physician supplies appeared to matter very much in the effective provision of cancer care in Canada. Community healthcare service endowments that include adequate physician supplies may be particularly critical to the performance of a healthcare system such as that in Canada, which provides universal accessibility to medically necessary care.

Keywords: physician supplies, primary care, general practitioners, family physicians, obstetrician/gynecologists, healthcare service endowments, breast cancer, stage at diagnosis, survival, Ontario, Canada

Research into Canada’s physician supply problem, whether it is real or merely perceived, has been nearly exclusively descriptive, with opinionated and often self-interested advocates typically debating the possible effects of various identified supply shortages. However, what are the actual sentinel, population-level health effects of any such developing shortages? Clearly, the rational development of evidence-based physician supply policies will require not only knowledge regarding prevalent changes in primary care and specialist physician supplies and practice patterns but also knowledge concerning the effects that any such changes may have on key population health indicators. Essentially, an answer still is needed to this field’s “so what?” question. Much already is known regarding physician supply trends in Canada, but very little is known regarding important physician supply/population health relations. The objective of this study was to begin to fill this critical policy-relevant knowledge gap.

Primary care physician supplies have been associated consistently and significantly with improved health outcomes (all-cause, cancer, heart disease, stroke, and infant mortality) over the past generation in the United States.1 Several US studies focused on a sentinel health indicator of great public health significance—breast cancer—and observed that community, typically county-level, primary care physician supplies were associated significantly with more prevalent screening mammography, more localized disease at diagnosis, and longer breast cancer survival.25 These advantages appeared to be fairly specific to primary care, and overall physician supplies generally were not predictive. We are not aware of any such Canadian physician supply/cancer care knowledge. It certainly appears plausible that, in a single-payer, universally accessible healthcare system such as that in Canada, community healthcare service endowments, a key element of which is physician supply, would be critical. In fact, having consistently observed that personal economic resources explain very little of the regional or temporal variability in Canadian cancer care, although they are highly predictive in the United States,611 our research group theorized that key community-level resources, such as physician supplies and other healthcare resources, would be even more predictive in Canada. Others have theorized that good primary care predicts not only more effective prevention but also more effective referral and continuity of care.1214 We therefore hypothesized the following: 1) Primary care physician supplies in Canada are associated significantly with localized breast cancer at the time of diagnosis and with more prevalent 5-year breast cancer survival (Hypothesis 1). 2) Regions in which primary care physician supplies had decreased significantly during the 1990s were significantly disadvantaged on both breast cancer stage at diagnosis and survival (Hypothesis 2).


A study of female breast cancer survival in Ontario provided population-based data for this retrospective cohort analysis of women ages ≥25 years who were diagnosed in the late 1980s (January 1, 1988 to December 31, 1990) or in the late 1990s (January 1, 1998 to December 31, 2000; International Classification of Diseases, 9th Edition code 174).10,11 The study originally was powered to detect a 15% difference in the survival rate between 3 socioeconomic strata within 3 types of places (α = .05 [2-tailed] and power [1 − β] = .80).15 Comprehensive and valid Ontario Cancer Registry (OCR) samples, stratified by 3 unique places, were selected randomly from the greater metropolitan Toronto (GMT) megalopolis, a relatively small metropolitan area (Windsor-Essex County) and small rural places with populations of <10,000 and population densities <400 individuals per km2.1625 Summary stage at the time of diagnosis was reliably abstracted from hospital and physician office-based patient charts to enhance the OCR database.26,27 Cases were joined to a census tract-based measure of socioeconomic status (prevalence of “low-income” households based on census subdivisions in rural areas) to account in part for personal economic status.1922,2830 Respective samples from the 1980s and 1990s samples of 879 and 951 invasive breast cancer cases were followed until January 1, 1996 and January 1, 2006, respectively. Organized breast cancer screening began in Canada in 1988,31 so systemic screening access differences are not likely to confound any cohort effects.

On the basis of the Scott’s Medical Database, Ontario active physician supply counts for the years 1991 and 2001 (and 2006 for descriptive purposes) were obtained from the Canadian Institute for Health Information (CIHI). A series of interagency validity checks (CIHI and Scott’s Directories) and CIHI edit checks ensured that error rates were almost nonexistent for all variables (only 0.2% for primary care physicians and specialists).32 Each physicians’ preferred business mailing address served as a proxy for their practice location. Primary care physicians or general practitioners (GPs) (physicians without a current medical specialty certified in Canada) included family medicine and emergency family medicine physicians. In addition, because they often provide primary care for women, the independent effects of those whose current medical specialty was obstetrics and gynecology (OB/GYN) were explored. Rates per 10,000 population for GPs and per 100,000 for OB/GYN specialists were calculated for Ontario’s 49 census divisions (CD), which correspond to counties, districts, or regional municipalities.19,20 When the original rural sample of breast cancer cases was reaggregated by CDs, it formed 2 rather distinct groups: places in which the majority reside in rural areas, as originally defined (rural), and other places, largely representative of the exurban fringes of Ontario’s other metropolitan areas (other). The predictive importance of these 2 groups was explored in the current study. Maximum likelihood logistic regression models were used to estimate the respective associations of 1991 and 2001 physician supplies with stage at diagnosis (localized vs regional or metastasized disease) and 5-year survival of patients with incident breast cancer diagnosed between 1988 and 1990 and between 1998 and 2000. Age-adjusted and income-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated from regression statistics.33 Because preliminary analyses suggested probable threshold effects, each incrementally higher physician supply category was compared with the average effect of the previous categories. In addition to maximizing statistical power, using reverse Helmert contrasts allowed for the identification of any such thresholds.33,34 Physician supply categories (physician integer increments per population standards) were constructed to maximize the comparability of the study’s 2 cohorts with each other as well as with previously studied cohorts and, thus, to maximize the intuitive policy interpretation of the findings.


Physician supply rate parameters are displayed in Table 1. First, the loss that the province of Ontario experienced during the 1990s of approximately 1.5 physicians per 10,000 population appears to have been maintained, essentially, up to the present. Second, it appears that this loss was nearly exclusively a loss of GPs. Specialist physician supplies did not change significantly, except in the Windsor metropolitan area, which lost approximately 1 such specialist per 10,000 population between 1991 and 2006. Third, the supply of GPs in rural areas, which already were relatively undersupplied in 1991, were unaltered for the most part during this era. Fourth and finally, on average, most nonrural areas of the province lost approximately 1 OB/GYN specialist physician per 100,000 population. However, the overall supply rates varied widely across the province’s 49 CDs or regions by a factor of 3, for example, for GPs (5 to 15 per 10,000 population) and by a factor of 10 for OB/GYN specialists (0 to 10 per 100,000 population) in 2001. The covariance of such physician supply variance with cancer care variance is examined below.

Table 1
Supply Rates of General Practitioner and Specialist Physicians by Place in Ontario

Ample support for Hypothesis 1 was observed among the late 1980s cohort (Table 2). Threshold effects were observed for both GPs (≥7 per 10,000 population) and OB/GYN specialists (≥6 per 100,000 population). Patients with breast cancer in areas that enjoyed such supplies were significantly more likely to be diagnosed with localized disease (GPs: OR, 1.58 [95% CI, 1.12–2.24] and OB/GYNs: OR, 1.59 [95% CI, 1.12–2.26]). In addition, the practically significant physician supply/5-year survival associations approached statistical significance (GPs: OR, 1.30 [95% CI, 0.96–1.76] and OB/GYNs: OR, 1.22 [95% CI, 0.83–1.79]). A generally attenuated and, for the most part, not statistically significant pattern was observed among the late 1990s cohort. It appeared that GP supply losses may have been large enough to diminish the overall population preventive impact of GPs on breast cancer care. The exception was that the highly significant OB/GYN supply/breast cancer survival effect was even larger than it had been a decade previously (OR, 1.99; 95% CI, 1.22–3.23). Perhaps when GP supplies diminish, certain specialists, such as OB/GYNs, increasingly fill primary care gaps.

Table 2
Associations of the Supply of General Practitioners and Obstetrician/Gynecologists With Localized Breast Cancer Stage at Diagnosis and 5-year Survival in Ontario*

The risk of living in undersupplied areas increased significantly during the 1990s: <7 GPs per 10,000 population (2001/1991 age-adjusted rate ratio [RR], 0.597/0.452 = 1.32; 95% CI, 1.21–1.44) and <6 OB/GYNs per 100,000 population (2001/11991 age-adjusted RR, 0.800/0.732 = 1.09; 95% CI, 1.02–1.14). No other physician supplies (additional primary care physicians [GP or OB/GYN] above identified thresholds, total physicians, or other specialists) added significantly to the explanatory power of any of the displayed models.

Observational support for Hypothesis 2 is displayed in Table 3. Women who were diagnosed with breast cancer in the late 1990s, who were followed until 2006, and who lived in regions in which primary care physician supplies (GPs and OB/GYNs) had decreased by <1 physician per 10,000 population during the 1990s were significantly more likely to be diagnosed with localized disease (OR, 1.60; 95% CI, 1.00–2.58) and to survive for >5 years (OR, 1.62; 95% CI, 1.03–2.55] than their counterparts in regions that experienced greater losses. After physician supply variables were accounted for, place (greater metropolitan Toronto, Windsor, rural, or other places), per se, did not enter any of the regression models.

Table 3
Associations of Changes in the Supply of Primary Care Physician With Localized Breast Cancer Stage at Diagnosis and 5-year Survival in Ontario*


In this retrospective cohort study, we observed significant threshold effects for GPs (7 per 10,000 population) and OB/GYNs (6 per 100,000 population) at or above which women with breast cancer were significantly more likely to have been diagnosed with localized disease and to have survived for ≥5 years. In addition, in an era of increased specialization, the evidence-based risk of living in such undersupplied areas increased significantly during the 1990s. The respective GP and OB/GYN 2001/1991 undersupply RRs were 1.32 and 1.09. This study also demonstrated that primary care physician losses during the 1990s were associated with significantly reduced cancer care protections. Consistent with this field’s historic-theoretical context,1214 this study’s physician supply stage and stage-adjusted physician supply/survival associations implicate both preventive effects and treatment effects. It appears likely that primary care physicians support more effective breast cancer screening as well as more effective initial and adjuvant treatment, most likely through their brokering of more effective specialist referrals, treatment advocacy, and ongoing follow-up.

Such clearly identified physician supply/health threshold effects sentinel policy hope that identified physician undersupplies can be rectified through rational, cost-effective planning. That is, beyond a certain necessary investment in provincial and national healthcare, including physician supplies, additional investments most likely will not necessarily pay greater population health dividends. However, we ought to continue to work toward building knowledge that allows us to identify and then make such necessary investments.

An exemplary look at a place that was identified clearly as experiencing a primary care physician shortage—Windsor/Essex County—may be instructive. During the 1990s, the Windsor metropolitan area moved from an evidence-based, adequate GP supply of 7 per 10,000 population in 1991 to only 5.8 per 10,000 population in 2001. With a population of 390,500 in 2001, 47 additional GPs would be needed to rectify the shortage. In fact, half of that shortage already had been filled by 2006. So, it could be estimated rationally and empirically that, at least in terms of maximizing cancer control and care in the area, approximately 23 more GPs would be needed. The similarly computed OB/GYN estimate would be 4 to 5 additional OB/GYNs. In addition to providing additional evidence for decision-making and policy planning, such reasonable estimates also may serve to direct the vaguer emotional responses that understandably sometimes accompany advocacy in this field.

The findings of the current study generally were consistent with the only other Canadian provincial study of which we are aware that explored a population-based physician supply/health relations.35 Notwithstanding its potential limitations (it was based on a cross-sectional assumption of a linear physician supply/health outcome relation, it was not adjusted for socioeconomic status, and it focused on mortality, which potentially confounded incidence and survival), the authors of that study observed modest primary care physician and cardiologist supply associations with cardiac morbidity, but not mortality. Perhaps not surprisingly, because they studied a different area of medical care—cardiovascular health services—those authors observed a different pattern of physician supply/population health relations than we observed by studying breast cancer care. There appear to be obvious policy-planning benefits for future, similar studies of primary and diverse specialist physician care across other prevalent health problems and healthcare domains.


This study’s sample of women with breast cancer is not necessarily representative of the province of Ontario as a whole, and its physician supply/cancer care findings may not be generalizable to all of its diverse places. Our original Ontario sampling frame randomly selected individuals from purposively diverse and potentially policy-important places, over-sampling large (Toronto) and small (Windsor) urban and rural places. Admittedly, our findings are most generalizable to such places. It should be noted, however, that, after accounting for key elements of health-care service endowments (that is, physician supplies), place, per se, did not seem to matter in any of this study’s analytic models. And because this study systematically replicated established physician supply trends in Ontario (increased specialization with identifiable geographic areas of undersupply), it did appear to be closely representative of the province’s population of active physicians.36,37 The physician counts in the current study were just that: “head counts” of active physicians. That approach conceivably may have been problematic, because it did not allow for the estimation of full-time physician equivalents, a measure of physician workload. In fact, it has been demonstrated that head-count data result in Canadian physician/population ratios that are overestimates of the truth; however, it also has been demonstrated that such overestimation is the least problematic in Ontario (5%–10%).38 Any such slight overestimation could be accounted for easily in planning future physician supplies.

The measures of physician supply that were used in the current study were CD aggregates and, thus, did not directly examine individual physician-patient relationships. However, those measures were conceived as proxies of community-level phenomena, that is, of regional healthcare service endowments, and we believe that tentative, population-level, policy-relevant inferences may be drawn most appropriately from this study, although any clinically relevant inferences made concerning the behaviors of physician’s themselves are thought of best as screened hypotheses that remain for future research testing. Finally, although this study was able to account for several important factors (age, income, place, and disease stage at diagnosis), it could not account for notable others such as marital status and race/ethnicity. However, previous studies by our research group and others710,39,40 have indicated consistently that marital status and race/ethnicity are cancer care gradients that tend to be quite steep in the United States tend to be nil to null in Canada. Therefore, we believe that such factors and their correlates most likely are not potent alternative explanations for the central physician supply/cancer care findings in the current study.

In conclusion, primary care physician supplies seem to matter very much in the effective provision of cancer care in Canada. Community healthcare service endowments that include adequate physician supplies may be particularly critical to the performance of a healthcare system such as that in Canada, which provides universal accessibility to medically necessary care.


Conflict of Interest Disclosures:

The authors made no disclosures.


1. Macinko J, Starfield B, Shi L. Is primary care effective? Quantifying the health benefits of primary care physician supply in the United States. Int J Health Serv. 2007;37:111–126. [PubMed]
2. Coughlin SS, Leadbetter S, Richards T, Sabatino SA. Contextual analysis of breast and cervical cancer screening and factors associated with health care access among United States women, 2002. Soc Sci Med. 2008;66:260–275. [PubMed]
3. Davidson PL, Bastani R, Nakazono TT, Carreon DC. Role of community risk factors and resources on breast carcinoma stage at diagnosis. Cancer. 2005;103:922–930. [PubMed]
4. Ferrante JM, Gonzalez EC, Pal N, Roetzheim RG. Effects of physician supply on early detection of breast cancer. J Am Board Fam Pract. 2000;13:408–414. [PubMed]
5. Fleisher JM, Lou JQ, Farrell M. Relationship between physician supply and breast cancer survival: a geographic approach. J Community Health. 2008;33:179–182. [PubMed]
6. Gorey KM, Fung KY, Luginaah IN, et al. Cancer survival in Ontario, 1986–2003: evidence of equitable advances across most diverse urban and rural places. Can J Public Health. 2008;99:12–16. [PMC free article] [PubMed]
7. Gorey KM, Kliewer E, Holowaty EJ, Laukkanen E, Ng EY. An international comparison of breast cancer survival: Winnipeg, Manitoba and Des Moines, Iowa, metropolitan areas. Ann Epidemiol. 2003;13:32–41. [PMC free article] [PubMed]
8. Gorey KM, Holowaty EJ, Fehringer G, Laukkanen E, Richter NL, Meyer CM. An international comparison of cancer survival: Metropolitan Toronto, Ontario and Honolulu, Hawaii. Am J Public Health. 2000;90:1866–1872. [PubMed]
9. Gorey KM, Holowaty EJ, Fehringer G, et al. An international comparison of cancer survival: Toronto, Ontario, and Detroit, Michigan, metropolitan areas. Am J Public Health. 1997;87:1156–1163. [PubMed]
10. Gorey KM. Breast cancer survival in Canada and the United States: meta-analytic evidence of a Canadian advantage in low-income areas. Int J Epidemiol. In press. [PMC free article] [PubMed]
11. Gorey KM, Luginaah IN, Holowaty EJ, Fung KY, Hamm C. Breast cancer survival in Ontario and California, 1998 to 2006: socioeconomic inequality remains much greater in the United States. Ann Epidemiol. 2009;19:121–124. [PMC free article] [PubMed]
12. Shi L, Macinko J, Starfield B, Politzer R, Wulu J, Xu J. Primary care, social inequalities, and all-cause, heart disease, and cancer mortality in US counties, 1990. Am J Public Health. 2005;95:674–680. [PubMed]
13. Macinko J, Starfield B, Shi L. The contribution of primary care systems to health outcomes within organization for economic cooperation and development (OECD) countries, 1970–1998. Health Serv Res. 2003;38:831–865. [PMC free article] [PubMed]
14. Menec VH, Sirski M, Attawar D. Does continuity of care matter in a universally insured population? Health Serv Res. 2005;40:389–400. [PMC free article] [PubMed]
15. Fleiss JL, Levin B, Paik MC. Statistical Methods for Rates and Proportions. 3. New York, NY: John Wiley & Sons, Inc; 2003.
16. Hall S, Schulze K, Groome P, Mackillop W, Holowaty E. Using cancer registry data for survival studies: the example of the Ontario Cancer Registry. J Clin Epidemiol. 2006;59:67–76. [PubMed]
17. Walter SD, Birnie SE, Marrett LD, et al. The geographic variation of cancer incidence in Ontario. Am J Public Health. 1994;84:367–376. [PubMed]
18. North American Association of Central Cancer Registries. Data quality assessments. [Accessed on July 12, 2008]. Available at:
19. Statistics Canada. Profiles of Census Divisions and Subdivisions, 2001 (Ontario) Ottawa, Ontario, Canada: Statistics Canada; 2002.
20. Statistics Canada. Profiles of Census Divisions and Subdivisions, 1991 (Ontario) Ottawa, Ontario, Canada: Statistics Canada; 1992.
21. Statistics Canada. Profiles of Census Tracts, 2001 (Ontario) Ottawa, Ontario, Canada: Statistics Canada; 2002.
22. Statistics Canada. Profiles of Census Tracts, 1991 (Ontario) Ottawa, Ontario, Canada: Statistics Canada; 1992.
23. Ministry of Health and Long-Term Care. Residence Coding Manual. Toronto, Ontario, Canada: Ministry of Health and Long-Term Care; 2003.
24. Statistics Canada. Definitions of “Rural”. Ottawa, Ontario, Canada: Statistics Canada; 2002.
25. Health Canada. Definitions of “Rural” Summary. Ottawa, Ontario, Canada: Statistics Canada; 2002.
26. Young JL Jr, Roffers SD, Ries LAG, Fritz AG, Hurlbut AA, editors. NIH Pub. No. 01-4969. Bethesda, Md: National Cancer Institute; 2001. SEER Summary Staging Manual–2000: Codes and Coding Instructions.
27. National Cancer Institute. NIH Pub. No. 98-1999. 3. Bethesda, Md: National Cancer Institute, National Institutes of Health; 1998. SEER Extent of Disease—1988 Codes and Coding Instructions.
28. Gorey KM. Regarding “ssociations between socioeconomic status and cancer survival” Ann Epidemiol. 2006;16:789–791. [PMC free article] [PubMed]
29. Krieger N, Chen JT, Waterman PD, Rehkopf DH, Subramanian SV. Race/ethnicity, gender, and monitoring socioeconomic gradients in health: a comparison of area-based socioeconomic measures—the Public Health Disparities Geocoding Project. Am J Public Health. 2003;93:1655–1671. [PubMed]
30. Krieger N, Chen JT, Waterman PD, Soobader M, Subramanian SV, Carson R. Geocoding and monitoring of US socioeconomic inequalities in mortality and cancer incidence: does the choice of area-based measure and geographic level matter? The Public Health Disparities Geocoding Project. Am J Epidemiol. 2002;156:471–482. [PubMed]
31. Wadden N, Doyle GP. Breast cancer screening in Canada: a review. Can Assoc Radiol J. 2005;56:271–175. [PubMed]
32. Canadian Institute for Health Information. Supply, Distribution and Migration of Canadian Physicians, 2006. Ottawa, Ontario, Canada: Canadian Institute for Health Information; 2007.
33. Hosmer DW, Lemeshow S. Applied Logistic Regression. 2. New York, NY: John Wiley & Sons, Inc; 2000.
34. Klockars AJ, Hancock GR. Power of recent multiple comparison procedures as applied to a complete set of planned orthogonal contrasts. Psych Bull. 1992;111:505–510.
35. Alter DA, Stukel TA, Newman A. The relationship between physician supply, cardiovascular health service use and cardiac disease burden in Ontario: supply-need mismatch. Can J Cardiol. 2008;24:187–193. [PMC free article] [PubMed]
36. Ontario Ministry of Health and Long Term Care. Expert Panel on Health Professional Human Resources. Toronto, Ontario, Canada: Ministry of Health and Long-Term Care; 2001. Shaping Ontario’s Physician Workforce.
37. Chan B. Supply of Physicians’ Services in Ontario. Toronto, Ontario, Canada: Institute for Clinical Evaluative Sciences; 1999.
38. Pong RW, Pitblado JR. Geographic Distribution of Physicians in Canada: Beyond How Many and Where. Ottawa, Ontario, Canada: Canadian Institute for Health Information; 2005.
39. Blackwell DL, Martinez ME, Gentleman JF. Women’s compliance with public health guidelines for mammograms and Pap tests in Canada and the United States: an analysis of data from the Joint Canada/United States Survey of Health. Womens Health Issues. 2008;18:85–99. [PubMed]
40. Ramirez AJ, Westcombe AM, Burgess CC, Sutton S, Littlejohns P, Richards MA. Factors predicting delayed presentation of symptomatic breast cancer: a systematic review. Lancet. 1999;353:1127–1131. [PubMed]