HEALTH SERVICES RESEARCH 0
RECHERCHE EN SERVICES DE SOINS DE SANTE
Small-area variations: What are they and what do they mean? Health Services Research Group In region A the rate of gallbladder surgery is five times that in region B. Government health officials express concern to surgeons in both regions. The surgeons in return ask: "What are small-area variations anyway, and what are their implications?" This article provides a brief introduction for clinicians interested in the problem of small-area variations (SAVs).
surgical admission rates. Roos, Wennberg and McPherson'0 examined medical and surgical hospital admission data across 30 hospital market areas in New England. Within each category (medical or surgical) admissions were ranked as to variation: low, moderate, high or very high." The reasons for medical admission that showed very high variation included chronic obstructive lung disease, peptic ulcer and hypertension. The surgical procedures showing very high variation included tonsillectomy, What are SAVs? dental extractions and knee operations. A closer SAVs are the large differences in the rates of use analysis'2"3 revealed that small areas in New Enof medical services (e.g., hospital admissions and gland or small hospital areas in Manitoba could be surgical or diagnostic procedures) between geograph- characterized by a "surgical signature"; that is, they ic regions. These variations have been noted in had high rates for some procedures but not for comparisons of countries,'2 provinces and states3-5 others. This surgical profile appeared to be consisand regions within a province.6 For example, the tent over time.'2 However, the rates of operative or rates of seven common surgical procedures varied diagnostic procedures for similar disorders (e.g., from threefold to sevenfold when Canada, the Unit- hysterectomy and tubal sterilization) tended to vary ed States, Norway, England and Wales were com- in a parallel fashion.4"4 Thus, geographic variations pared.7 In Canada there were wide variations be- in the use of hospitals (whether counted as number tween the provinces in the rates of 16 operations,5 of admissions, number of patient-days, length of and within one province the rates of all surgical stay, average expenditure per patient or death rate) procedures varied from 74.7 to 115.2 procedures per and in medical and dental services have been found 1000 elderly patients.8 In another province the rate whenever they have been sought.'5 of coronary artery bypass surgery varied from 28 to 94 procedures per 100 000 population.9 When com- Why are SAVs important? paring the rates of common operations such as It has been argued that people who live in areas hysterectomy and cholecystectomy across countries McPherson7 found large differences in the absolute where surgical or hospital admission rates are very rate of their performance. However, the operations high may be undergoing unnecessary treatment, with that showed large (or small) variations in one coun- the risks of iatrogenic illness and postoperative death. Conversely, people who live in areas where try showed similar variations in the other countries. Variations have been shown in medical and such rates are low may not be receiving the benefits
Members: Drs. Marsha M. Cohen (principal author), Department ofHealth Administration; C. David Naylor, Department ofMedicine; Antoni S.H. Basinski, Department ofFamily and Community Medicine; Lorraine E. Ferris, Department ofBehavioural Science; Hilary A. Llewellyn-Thomas, Faculty ofNursing; and J. Ivan Williams, Department of Preventive Medicine and Biostatistics, University of Toronto, Toronto, Ont. The Health Services Research Group is part of the Clinical Epidemiology Unit, Sunnybrook Health Science Centre, Toronto, Ont. Reprint requests to: Health Services Research Group, Clinical Epidemiology Unit, Rm. A443, Sunnybrook Health Science Centre, 2075 Bayview Ave., Toronto, ON M4N 3M5 FEBRUARY 15, 1992
CAN MED ASSOC J 1992; 146 (4)
467
of modem medical services, and there may be a problem of access to care. As well, policy-makers and ethicists are concerned about variations in medical care in an era of limited health care dollars. The overly high rates in some areas suggest misallocation of limited resources. Wennbergl" argued that if the overall rate of hysterectomy in Maine in 1982 were the same as that in the low-rate areas, then the savings to the health care system would be about $10 million for that procedure alone. However, no one can agree on which rate is optimal and which rate represents appropriate care. The vexing question remains Is it possible to define a correct rate?
Therefore, there is a trade-off between the homogeneity of the population in a very small geographic area and the stable rates in a larger region with bigger numerators and denominators. Some of the variation in the rates of medical or surgical services can be explained by differences in age and sex in the populations; for example, there will be more hip replacements done in Victoria than in Whitehorse. Therefore, adjustments must be made for age and sex before the rates are examined for variations. Also, statistical tests are applied to rule out the possibility of random fluctuations.2",9120
How are SAVs determined?
What causes SAVs?
SAVs are analysed by means of well-established
There is a general belief that medical care is
epidemiologic methods.2 The rates of hospital admis- based on scientific evidence and that the clinical sions and surgical or diagnostic procedures (or other decisions about the treatment of a particular conmedical services of interest) are calculated after the dition should be similar. The finding of large differnumerator and denominator of the rates usually ences in the rates of diagnosis and of medical and derived from administrative databases (i.e., data surgical treatment is important because it questions routinely collected for payment of medical insur- this assumption. The reasons for the variations ance) are determined (Table 1). Although at first this remain a subject of active research. may appear obvious there are other methods for determining the rates. Some investigators9"'0"12 used the hospital market area as the unit of analysis. Medical records for each hospital in New England were examined for the areas of residence of most of the patients admitted. Thereafter, all the people living in those areas were "assigned" to that hospital even if it was not the one they were admitted to. Others1'6'4 used the residence of patients as the unit of analysis and determined the rates of use by those admitted to hospital, regardless of the location of treatment. If the number of procedures or the population at risk for that procedure in an area is small, then the rates may be statistically unstable; that is, a few procedures can markedly alter the rate.
Although everyone agrees that SAVs exist there is much controversy about what causes them. Underlying differences in the incidence and prevalence of disease may explain some of the variation. A high burden of disease in an area would explain the high rate of hospital admission for that condition. However, the burden of disease is not easily measured. If high enough, rates of death from a particular condition may suffice, but a measure of illness is much more complex, and definitions are rarely agreed on. As an alternative some researchers have used population surveys to determine disease rates. So far, studies have not confirmed that differences in disease rates explain variations in the rates of use of medical services, but these studies have been limited
Table : Stepsandissuesinanalysingsa *~~~~~~~~~~~~..ab
ra
n ..s.......
i:alans.....n
1 ssues
1. Determ.i.natin of rs.... ;: . .num ~~~~~~~~. . . .....
..
Accuracyocd ng diagnos.e and Potential fr double-counting (especiallysti of. medica admissions)'7: ncluson of province procedures.
3. Stblzto of... 0 ...... egahicreins: Whatsize?'8. .. .-....
........
.Hospital market..... areas: selection of...... . . . ~~~~~~~~~~~~~~~... .......
sasc :.sts
*Tr..ade-off between stablity (in..large
and homogeneity (in. geographi areas) ..... ~~~~~~~~~~~~...:.::..
:
of 5.* . ...... Application ......... ......X-...
C
468
CAN MED ASSOC J 1992; 146 (4)
i .o r
f
. : ~~~ntron.. ..Co .f....random.fha ions.... 9.........
a i
LE 1 5 FEVRIER 1992
in number. Wennberg and Gittelsohn12 surveyed households in six adjacent hospital markets in Maine and, despite large differences in hospital use across these areas, found no differences in the disease rates. Roos and associates2' also found that differences in the characteristics of elderly patients in Manitoba did not explain the differences in the rates of hospital admission. Other potential contributors to SAVs may be differences in the socioeconomic or ethnic characteristics of the population. It is now recognized that Canadians in lower-income groups have higher rates of illness and death than those in other income groups. Thus, if a region has a high proportion of people living in poverty it presumably should show high rates of use of many medical services and procedures. Studies that have examined socioeconomic factors have had mixed findings. One study used a multivariate analysis (which examines each factor under consideration while controlling for all others) and revealed that the levels of education, income, poverty and unemployment of a region's population do explain a significant proportion of the variation in medical and surgical admission rates.22 However, even when this source of variation is taken into account there are still differences in the rates. The effect on SAVs of ethnic background in small regions has not been studied to date. Another factor believed to contribute to SAVs is the supply of health care resources in an area. Here again studies have had inconsistent results. Early studies related the variations in surgical rates to the supply of hospital beds, the number of surgeons and the mode of physician or surgeon payment (fee for service v. salary).2"12'23 Thus, the higher proportion of physicians and hospital beds in the United States than in Britain would explain the higher US rates of use. Other studies have confirmed the importance of some but not all of these factors.6'22 One recent study found that after health indicators, socioeconomic characteristics and the surgical styles of physicians were considered, variations in discharge rates after surgery among elderly patients were related to the supply of medical resources.24 Leape and collaborators25 found that the geographic variation in the rate of use of carotid endarterectomy was due to a few surgeons who performed large numbers of operations. Despite mixed evidence it appears that most of the studies support the conclusion that the supply of health care resources has an effect on SAVs. A potential explanation for high rates of use of medical services in a small area is the inappropriate provision of the index procedure or service. Researchers at the Rand Corporation26'27 examined the appropriateness of coronary angiography, carotid endarterectomy and endoscopy of the upper gastrointestinal tract across geographic areas where the FEBRUARY 15, 1992
rates of use of these procedures were high, average and low. A detailed review of medical records was carried out, and each case was assigned an appropriateness rating. Some relation was found between inappropriateness and high rates of use. However, the relation was too weak to account for the wide variations in the rates across the regions. The authors concluded that differences in appropriateness could not explain the SAVs, at least with respect to these three procedures. Wennberg"1 stated that one of the most important factors affecting SAVs is physician practice style and a lack of consensus on the diagnosis and treatment of many conditions. Some physicians choose to manage a patient conservatively (watchful waiting), whereas others would admit the same patient to hospital and perhaps perform a diagnostic or surgical procedure. Some examples in the field of coronary artery disease illustrate this point. Naylor and colleagues28 found that among a panel of 16 cardiologists and cardiac surgeons asked to rate 438 cases in which patients awaited coronary revascularization there was only modest agreement as to the urgency of the cases. Brook and coworkers29 found marked differences between panels of US and British physicians in their ratings of the appropriateness of indications for coronary angiography and bypass surgery. For coronary artery bypass surgery 13% of the indications were rated as inappropriate by the US physicians, as compared with 35% by the British physicians. Factors contributing to physician practice style include physician or patient convenience, the practice of defensive medicine and physician training and referral patterns. Wennberg"1 pointed out that when there is consensus in the medical profession there is little variation in the use of hospitals or surgical procedures, as in the case of inguinal hernia, acute myocardial infarction and hip fractures. The mode of treatment for these conditions is relatively straightforward in that all patients would receive treatment in hospital. The variations are high for conditions for which there is less consensus, such as back problems, dental extractions and asthma in adults.'0 The hypothesis about physician practice style is not without its critics.'8 Eisenberg30 argued that the factors affecting physician practice style are complex and multifactorial and involve an interaction between the physician's training, practice variables, personal desires, income goals and actions in the best interests of patients. Folland and Stano3' did not confirm that practice style was important in determining rates of hospital market use or the intensity with which individual patients are treated by physicians. Roos,32 on the other hand, found that after taking into account the population mix of patieints in physicians' practices in Manitoba the most important factor predicting the CAN MED ASSOC J 1992; 146 (4)
469
hospital admission of an elderly person was whether his or her physician was a high user of hospitals.
Conclusions SAVs exist for most medical services, including many diagnostic and therapeutic procedures. These variations raise the issues of poor access to health care or inappropriate underutilization of health care resources in some areas and of the iatrogenic consequences of overutilization in others. It is imperative that physicians and administrators take the initiative to examine data from their regions or hospitals as part of quality management practices and compare their data with those of others on a local, provincial and national scale. To determine fairly what causes SAVs an intensive examination may be necessary to discover the local contribution and to implement interventions for change. Uncertainty in clinical decision-making contributes greatly to SAVs. Wennberg" called for more informed clinical decision-making, more clinical trials, the establishment of guidelines and standards and better undergraduate and postgraduate education. There is a need to establish better criteria to determine what care is appropriate, necessary, desirable or of uncertain value. Also, there should be more research into the relation between practice styles, regional variations and treatment outcomes, as well as into the reasons for the variations and what strategies are effective in reducing them.33 The goal is not to eliminate individualized decision-making but, rather, to address the problem of radically different rates of use of common services by explaining the root causes.
References 1. Vayda E: A comparison of surgical rates in Canada and in
England and Wales. NEngl JMed 1973; 289: 1224-1229 2. McPherson K, Wennberg JE, Hovind OB et al: Small-area variations in the use of common surgical procedures: an international comparison of New England, England and Norway. NEngl JMed 1982; 307: 1310-1314 3. Peters S, Chagani K, Paddon P et al: Coronary artery bypass surgery in Canada. Health Rep 1990; 2: 9-26 4. Chassin MR, Brook RH, Park RE et al: Variations in the use of medical and surgical services by the Medicare population. N Engl J Med 1986; 314: 285-290 5. Mindell WR, Vayda E, Cardillo B: Ten-year trends in Canada for selected operations. Can Med Assoc J 1982; 127: 23-27 6. Roos NP, Roos LL: Surgical rate variations: Do they reflect the health or socioeconomic characteristics of the population? Med Care 1982; 20: 945-958 7. McPherson K: Why do variations occur? In Andersen TF, Mooney G (eds): The Challenges of Medical Practice Variations, Macmillan, London, 1990: 16-35 8. Roos NP, Roos LL: High and low surgical rates: risk factors for area residents. Am J Public Health 1981; 71: 591-600 9. Anderson GM, Lomas J: Regionalization of coronary artery bypass surgery: effects on access. Med Care 1989; 27: 288296 470
CAN MED ASSOC J 1992; 146 (4)
10. Roos NP, Wennberg JE, McPherson K: Using diagnosis-related groups for studying variations in hospital admissions. Health Care Financ Rev 1988; 9: 53-61 11. Wennberg JE: Dealing with medical practice variations: a proposal for action. Health Aff 1984; 4: 6-32 12. Wennberg JE, Gittelsohn A: Variations in medical care among small areas. Sci Am 1982; 246: 120-134 13. Roos LL: Supply, workload and utilization: a populationbased analysis of surgery in rural Manitoba. Am J Public Health 1983; 73: 414-421 14. Cohen MM: Tubal sterilization in Manitoba. Can J Public Health 1986; 77: 114-118 15. Paul-Shaheen P, Clark JD, Williams D: Small area analysis: a review and analysis of the North American literature. J Health Polit Policy Law 1987; 12: 741-809 16. Roos LL, Sharp SM, Wajda A: Assessing data quality: a computerized approach. Soc Sci Med 1989; 28: 175-182 17. Van Walraven C, Wang B, Ugnat AM et al: False-positive coding for acute myocardial infarction on hospital discharge records: chart audit results from a tertiary centre. Can J Cardiol 1990; 6: 383-386 18. Folland S, Stano M: Small area variations: a critical review of propositions, methods and evidence. Med Care Rev 1990; 47: 419-465 19. Diehr P, Cain K, Connell T et al: What is too much variation? The null hypothesis in small-area analysis. Health Serv Res 1990; 24: 741-771 20. Diehr P: Small area statistics: large statistical problems. Am J Public Health 1984; 74: 313-314 21. Roos NP, Flowerdew G, Wajda A et al: Variations in physicians' hospitalization practices: a population-based study in Manitoba, Canada. Am J Public Health 1986; 76: 45-51 22. McLaughlin CG, Normolle DP, Wolfe RA et al: Small-area variation in hospital discharge rates: Do socioeconomic variables matter? Med Care 1989; 27: 507-521 23. Vayda E, Barnsley JM, Mindell WR et al: Five-year study of surgical rates in Ontario's counties. Can Med Assoc J 1984; 131: 111-115 24. Pasley B, Vernon P, Gibson G et al: Geographic variations in elderly hospital and surgical discharge rates, New York State. Am J Public Health 1987; 77: 679-684 25. Leape LL, Park RE, Solomon DH et al: Relation between surgeons' practice volumes and geographic variation in the rate of carotid endarterectomy. N Engl J Med 1989; 321: 653-657 26. Chassin MR, Kosecoff J, Park RE et al: Does inappropriate use explain geographic variations in the use of health care services? A study of three procedures. JAMA 1987; 258: 2533-2537 27. Leape LL, Park RE, Solomon DH et al: Does inappropriate use explain small-area variations in the use of health care services? JAMA 1990; 263: 669-672 28. Naylor CD, Basinski A, Baigrie RS et al: Placing patients in the queue for coronary revascularization: evidence for practice variations from an expert panel process. Am J Public Health 1990; 80: 1246-1252 29. Brook RH, Park RE, Winslow CM et al: Diagnosis and treatment of coronary disease: comparisons of doctors' attitudes in the USA and the UK. Lancet 1988; 1: 750-753 30. Eisenberg JM: Physician utilization: the state of research about physicians' practice patterns. Med Care 1985; 23: 461483 31. Folland S, Stano M: Sources of small area variations in the use of medical care. J Health Econ 1989; 8: 85-107 32. Roos NP: Predicting hospital utilization by the elderly: the importance of patient, physician and hospital characteristics. Med Care 1989; 27: 905-919 33. Andersen TF, Mooney G: Medical practice variations: Where are we? In Andersen TF, Mooney G (eds): The Challenges of MIedical Practice Variations, Macmillan, London, 1990: 1 -15 For prescribing information see page 592
RECHERCHE EN SERVICES DE SOINS DE SANTE
Small-area variations: What are they and what do they mean? Health Services Research Group In region A the rate of gallbladder surgery is five times that in region B. Government health officials express concern to surgeons in both regions. The surgeons in return ask: "What are small-area variations anyway, and what are their implications?" This article provides a brief introduction for clinicians interested in the problem of small-area variations (SAVs).
surgical admission rates. Roos, Wennberg and McPherson'0 examined medical and surgical hospital admission data across 30 hospital market areas in New England. Within each category (medical or surgical) admissions were ranked as to variation: low, moderate, high or very high." The reasons for medical admission that showed very high variation included chronic obstructive lung disease, peptic ulcer and hypertension. The surgical procedures showing very high variation included tonsillectomy, What are SAVs? dental extractions and knee operations. A closer SAVs are the large differences in the rates of use analysis'2"3 revealed that small areas in New Enof medical services (e.g., hospital admissions and gland or small hospital areas in Manitoba could be surgical or diagnostic procedures) between geograph- characterized by a "surgical signature"; that is, they ic regions. These variations have been noted in had high rates for some procedures but not for comparisons of countries,'2 provinces and states3-5 others. This surgical profile appeared to be consisand regions within a province.6 For example, the tent over time.'2 However, the rates of operative or rates of seven common surgical procedures varied diagnostic procedures for similar disorders (e.g., from threefold to sevenfold when Canada, the Unit- hysterectomy and tubal sterilization) tended to vary ed States, Norway, England and Wales were com- in a parallel fashion.4"4 Thus, geographic variations pared.7 In Canada there were wide variations be- in the use of hospitals (whether counted as number tween the provinces in the rates of 16 operations,5 of admissions, number of patient-days, length of and within one province the rates of all surgical stay, average expenditure per patient or death rate) procedures varied from 74.7 to 115.2 procedures per and in medical and dental services have been found 1000 elderly patients.8 In another province the rate whenever they have been sought.'5 of coronary artery bypass surgery varied from 28 to 94 procedures per 100 000 population.9 When com- Why are SAVs important? paring the rates of common operations such as It has been argued that people who live in areas hysterectomy and cholecystectomy across countries McPherson7 found large differences in the absolute where surgical or hospital admission rates are very rate of their performance. However, the operations high may be undergoing unnecessary treatment, with that showed large (or small) variations in one coun- the risks of iatrogenic illness and postoperative death. Conversely, people who live in areas where try showed similar variations in the other countries. Variations have been shown in medical and such rates are low may not be receiving the benefits
Members: Drs. Marsha M. Cohen (principal author), Department ofHealth Administration; C. David Naylor, Department ofMedicine; Antoni S.H. Basinski, Department ofFamily and Community Medicine; Lorraine E. Ferris, Department ofBehavioural Science; Hilary A. Llewellyn-Thomas, Faculty ofNursing; and J. Ivan Williams, Department of Preventive Medicine and Biostatistics, University of Toronto, Toronto, Ont. The Health Services Research Group is part of the Clinical Epidemiology Unit, Sunnybrook Health Science Centre, Toronto, Ont. Reprint requests to: Health Services Research Group, Clinical Epidemiology Unit, Rm. A443, Sunnybrook Health Science Centre, 2075 Bayview Ave., Toronto, ON M4N 3M5 FEBRUARY 15, 1992
CAN MED ASSOC J 1992; 146 (4)
467
of modem medical services, and there may be a problem of access to care. As well, policy-makers and ethicists are concerned about variations in medical care in an era of limited health care dollars. The overly high rates in some areas suggest misallocation of limited resources. Wennbergl" argued that if the overall rate of hysterectomy in Maine in 1982 were the same as that in the low-rate areas, then the savings to the health care system would be about $10 million for that procedure alone. However, no one can agree on which rate is optimal and which rate represents appropriate care. The vexing question remains Is it possible to define a correct rate?
Therefore, there is a trade-off between the homogeneity of the population in a very small geographic area and the stable rates in a larger region with bigger numerators and denominators. Some of the variation in the rates of medical or surgical services can be explained by differences in age and sex in the populations; for example, there will be more hip replacements done in Victoria than in Whitehorse. Therefore, adjustments must be made for age and sex before the rates are examined for variations. Also, statistical tests are applied to rule out the possibility of random fluctuations.2",9120
How are SAVs determined?
What causes SAVs?
SAVs are analysed by means of well-established
There is a general belief that medical care is
epidemiologic methods.2 The rates of hospital admis- based on scientific evidence and that the clinical sions and surgical or diagnostic procedures (or other decisions about the treatment of a particular conmedical services of interest) are calculated after the dition should be similar. The finding of large differnumerator and denominator of the rates usually ences in the rates of diagnosis and of medical and derived from administrative databases (i.e., data surgical treatment is important because it questions routinely collected for payment of medical insur- this assumption. The reasons for the variations ance) are determined (Table 1). Although at first this remain a subject of active research. may appear obvious there are other methods for determining the rates. Some investigators9"'0"12 used the hospital market area as the unit of analysis. Medical records for each hospital in New England were examined for the areas of residence of most of the patients admitted. Thereafter, all the people living in those areas were "assigned" to that hospital even if it was not the one they were admitted to. Others1'6'4 used the residence of patients as the unit of analysis and determined the rates of use by those admitted to hospital, regardless of the location of treatment. If the number of procedures or the population at risk for that procedure in an area is small, then the rates may be statistically unstable; that is, a few procedures can markedly alter the rate.
Although everyone agrees that SAVs exist there is much controversy about what causes them. Underlying differences in the incidence and prevalence of disease may explain some of the variation. A high burden of disease in an area would explain the high rate of hospital admission for that condition. However, the burden of disease is not easily measured. If high enough, rates of death from a particular condition may suffice, but a measure of illness is much more complex, and definitions are rarely agreed on. As an alternative some researchers have used population surveys to determine disease rates. So far, studies have not confirmed that differences in disease rates explain variations in the rates of use of medical services, but these studies have been limited
Table : Stepsandissuesinanalysingsa *~~~~~~~~~~~~..ab
ra
n ..s.......
i:alans.....n
1 ssues
1. Determ.i.natin of rs.... ;: . .num ~~~~~~~~. . . .....
..
Accuracyocd ng diagnos.e and Potential fr double-counting (especiallysti of. medica admissions)'7: ncluson of province procedures.
3. Stblzto of... 0 ...... egahicreins: Whatsize?'8. .. .-....
........
.Hospital market..... areas: selection of...... . . . ~~~~~~~~~~~~~~~... .......
sasc :.sts
*Tr..ade-off between stablity (in..large
and homogeneity (in. geographi areas) ..... ~~~~~~~~~~~~...:.::..
:
of 5.* . ...... Application ......... ......X-...
C
468
CAN MED ASSOC J 1992; 146 (4)
i .o r
f
. : ~~~ntron.. ..Co .f....random.fha ions.... 9.........
a i
LE 1 5 FEVRIER 1992
in number. Wennberg and Gittelsohn12 surveyed households in six adjacent hospital markets in Maine and, despite large differences in hospital use across these areas, found no differences in the disease rates. Roos and associates2' also found that differences in the characteristics of elderly patients in Manitoba did not explain the differences in the rates of hospital admission. Other potential contributors to SAVs may be differences in the socioeconomic or ethnic characteristics of the population. It is now recognized that Canadians in lower-income groups have higher rates of illness and death than those in other income groups. Thus, if a region has a high proportion of people living in poverty it presumably should show high rates of use of many medical services and procedures. Studies that have examined socioeconomic factors have had mixed findings. One study used a multivariate analysis (which examines each factor under consideration while controlling for all others) and revealed that the levels of education, income, poverty and unemployment of a region's population do explain a significant proportion of the variation in medical and surgical admission rates.22 However, even when this source of variation is taken into account there are still differences in the rates. The effect on SAVs of ethnic background in small regions has not been studied to date. Another factor believed to contribute to SAVs is the supply of health care resources in an area. Here again studies have had inconsistent results. Early studies related the variations in surgical rates to the supply of hospital beds, the number of surgeons and the mode of physician or surgeon payment (fee for service v. salary).2"12'23 Thus, the higher proportion of physicians and hospital beds in the United States than in Britain would explain the higher US rates of use. Other studies have confirmed the importance of some but not all of these factors.6'22 One recent study found that after health indicators, socioeconomic characteristics and the surgical styles of physicians were considered, variations in discharge rates after surgery among elderly patients were related to the supply of medical resources.24 Leape and collaborators25 found that the geographic variation in the rate of use of carotid endarterectomy was due to a few surgeons who performed large numbers of operations. Despite mixed evidence it appears that most of the studies support the conclusion that the supply of health care resources has an effect on SAVs. A potential explanation for high rates of use of medical services in a small area is the inappropriate provision of the index procedure or service. Researchers at the Rand Corporation26'27 examined the appropriateness of coronary angiography, carotid endarterectomy and endoscopy of the upper gastrointestinal tract across geographic areas where the FEBRUARY 15, 1992
rates of use of these procedures were high, average and low. A detailed review of medical records was carried out, and each case was assigned an appropriateness rating. Some relation was found between inappropriateness and high rates of use. However, the relation was too weak to account for the wide variations in the rates across the regions. The authors concluded that differences in appropriateness could not explain the SAVs, at least with respect to these three procedures. Wennberg"1 stated that one of the most important factors affecting SAVs is physician practice style and a lack of consensus on the diagnosis and treatment of many conditions. Some physicians choose to manage a patient conservatively (watchful waiting), whereas others would admit the same patient to hospital and perhaps perform a diagnostic or surgical procedure. Some examples in the field of coronary artery disease illustrate this point. Naylor and colleagues28 found that among a panel of 16 cardiologists and cardiac surgeons asked to rate 438 cases in which patients awaited coronary revascularization there was only modest agreement as to the urgency of the cases. Brook and coworkers29 found marked differences between panels of US and British physicians in their ratings of the appropriateness of indications for coronary angiography and bypass surgery. For coronary artery bypass surgery 13% of the indications were rated as inappropriate by the US physicians, as compared with 35% by the British physicians. Factors contributing to physician practice style include physician or patient convenience, the practice of defensive medicine and physician training and referral patterns. Wennberg"1 pointed out that when there is consensus in the medical profession there is little variation in the use of hospitals or surgical procedures, as in the case of inguinal hernia, acute myocardial infarction and hip fractures. The mode of treatment for these conditions is relatively straightforward in that all patients would receive treatment in hospital. The variations are high for conditions for which there is less consensus, such as back problems, dental extractions and asthma in adults.'0 The hypothesis about physician practice style is not without its critics.'8 Eisenberg30 argued that the factors affecting physician practice style are complex and multifactorial and involve an interaction between the physician's training, practice variables, personal desires, income goals and actions in the best interests of patients. Folland and Stano3' did not confirm that practice style was important in determining rates of hospital market use or the intensity with which individual patients are treated by physicians. Roos,32 on the other hand, found that after taking into account the population mix of patieints in physicians' practices in Manitoba the most important factor predicting the CAN MED ASSOC J 1992; 146 (4)
469
hospital admission of an elderly person was whether his or her physician was a high user of hospitals.
Conclusions SAVs exist for most medical services, including many diagnostic and therapeutic procedures. These variations raise the issues of poor access to health care or inappropriate underutilization of health care resources in some areas and of the iatrogenic consequences of overutilization in others. It is imperative that physicians and administrators take the initiative to examine data from their regions or hospitals as part of quality management practices and compare their data with those of others on a local, provincial and national scale. To determine fairly what causes SAVs an intensive examination may be necessary to discover the local contribution and to implement interventions for change. Uncertainty in clinical decision-making contributes greatly to SAVs. Wennberg" called for more informed clinical decision-making, more clinical trials, the establishment of guidelines and standards and better undergraduate and postgraduate education. There is a need to establish better criteria to determine what care is appropriate, necessary, desirable or of uncertain value. Also, there should be more research into the relation between practice styles, regional variations and treatment outcomes, as well as into the reasons for the variations and what strategies are effective in reducing them.33 The goal is not to eliminate individualized decision-making but, rather, to address the problem of radically different rates of use of common services by explaining the root causes.
References 1. Vayda E: A comparison of surgical rates in Canada and in
England and Wales. NEngl JMed 1973; 289: 1224-1229 2. McPherson K, Wennberg JE, Hovind OB et al: Small-area variations in the use of common surgical procedures: an international comparison of New England, England and Norway. NEngl JMed 1982; 307: 1310-1314 3. Peters S, Chagani K, Paddon P et al: Coronary artery bypass surgery in Canada. Health Rep 1990; 2: 9-26 4. Chassin MR, Brook RH, Park RE et al: Variations in the use of medical and surgical services by the Medicare population. N Engl J Med 1986; 314: 285-290 5. Mindell WR, Vayda E, Cardillo B: Ten-year trends in Canada for selected operations. Can Med Assoc J 1982; 127: 23-27 6. Roos NP, Roos LL: Surgical rate variations: Do they reflect the health or socioeconomic characteristics of the population? Med Care 1982; 20: 945-958 7. McPherson K: Why do variations occur? In Andersen TF, Mooney G (eds): The Challenges of Medical Practice Variations, Macmillan, London, 1990: 16-35 8. Roos NP, Roos LL: High and low surgical rates: risk factors for area residents. Am J Public Health 1981; 71: 591-600 9. Anderson GM, Lomas J: Regionalization of coronary artery bypass surgery: effects on access. Med Care 1989; 27: 288296 470
CAN MED ASSOC J 1992; 146 (4)
10. Roos NP, Wennberg JE, McPherson K: Using diagnosis-related groups for studying variations in hospital admissions. Health Care Financ Rev 1988; 9: 53-61 11. Wennberg JE: Dealing with medical practice variations: a proposal for action. Health Aff 1984; 4: 6-32 12. Wennberg JE, Gittelsohn A: Variations in medical care among small areas. Sci Am 1982; 246: 120-134 13. Roos LL: Supply, workload and utilization: a populationbased analysis of surgery in rural Manitoba. Am J Public Health 1983; 73: 414-421 14. Cohen MM: Tubal sterilization in Manitoba. Can J Public Health 1986; 77: 114-118 15. Paul-Shaheen P, Clark JD, Williams D: Small area analysis: a review and analysis of the North American literature. J Health Polit Policy Law 1987; 12: 741-809 16. Roos LL, Sharp SM, Wajda A: Assessing data quality: a computerized approach. Soc Sci Med 1989; 28: 175-182 17. Van Walraven C, Wang B, Ugnat AM et al: False-positive coding for acute myocardial infarction on hospital discharge records: chart audit results from a tertiary centre. Can J Cardiol 1990; 6: 383-386 18. Folland S, Stano M: Small area variations: a critical review of propositions, methods and evidence. Med Care Rev 1990; 47: 419-465 19. Diehr P, Cain K, Connell T et al: What is too much variation? The null hypothesis in small-area analysis. Health Serv Res 1990; 24: 741-771 20. Diehr P: Small area statistics: large statistical problems. Am J Public Health 1984; 74: 313-314 21. Roos NP, Flowerdew G, Wajda A et al: Variations in physicians' hospitalization practices: a population-based study in Manitoba, Canada. Am J Public Health 1986; 76: 45-51 22. McLaughlin CG, Normolle DP, Wolfe RA et al: Small-area variation in hospital discharge rates: Do socioeconomic variables matter? Med Care 1989; 27: 507-521 23. Vayda E, Barnsley JM, Mindell WR et al: Five-year study of surgical rates in Ontario's counties. Can Med Assoc J 1984; 131: 111-115 24. Pasley B, Vernon P, Gibson G et al: Geographic variations in elderly hospital and surgical discharge rates, New York State. Am J Public Health 1987; 77: 679-684 25. Leape LL, Park RE, Solomon DH et al: Relation between surgeons' practice volumes and geographic variation in the rate of carotid endarterectomy. N Engl J Med 1989; 321: 653-657 26. Chassin MR, Kosecoff J, Park RE et al: Does inappropriate use explain geographic variations in the use of health care services? A study of three procedures. JAMA 1987; 258: 2533-2537 27. Leape LL, Park RE, Solomon DH et al: Does inappropriate use explain small-area variations in the use of health care services? JAMA 1990; 263: 669-672 28. Naylor CD, Basinski A, Baigrie RS et al: Placing patients in the queue for coronary revascularization: evidence for practice variations from an expert panel process. Am J Public Health 1990; 80: 1246-1252 29. Brook RH, Park RE, Winslow CM et al: Diagnosis and treatment of coronary disease: comparisons of doctors' attitudes in the USA and the UK. Lancet 1988; 1: 750-753 30. Eisenberg JM: Physician utilization: the state of research about physicians' practice patterns. Med Care 1985; 23: 461483 31. Folland S, Stano M: Sources of small area variations in the use of medical care. J Health Econ 1989; 8: 85-107 32. Roos NP: Predicting hospital utilization by the elderly: the importance of patient, physician and hospital characteristics. Med Care 1989; 27: 905-919 33. Andersen TF, Mooney G: Medical practice variations: Where are we? In Andersen TF, Mooney G (eds): The Challenges of MIedical Practice Variations, Macmillan, London, 1990: 1 -15 For prescribing information see page 592
