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Original Contribution |

Physician and Population Determinants of Rates of Middle-Ear Surgery in Ontario FREE

Peter C. Coyte, PhD; Ruth Croxford, MSc; Carl V. Asche, MSc; Teresa To, PhD; William Feldman, MD, FRCPC; Jacob Friedberg, MD, FRCSC
[+] Author Affiliations

Author Affiliations: Departments of Health Policy, Management, and Evaluation (Dr Coyte and Mr Asche), Otolaryngology (Dr Friedberg), Pediatrics (Dr Feldman), and Public Health Sciences (Dr To), and the Institute for Policy Analysis (Dr Coyte), University of Toronto, Toronto, Ontario; Institute for Clinical Evaluative Sciences, Toronto (Drs Coyte and To); Clinical Epidemiology Unit, Sunnybrook and Women's College Health Science Centre, Toronto (Ms Croxford); Department of Otolaryngology (Drs Coyte and Friedberg), Mount Sinai Hospital, Toronto; and the Departments of Otolaryngology (Dr Friedberg) and General Pediatrics (Dr Feldman), Hospital for Sick Children, Toronto. Mr Asche is now with Aventis Pharmaceuticals, Bridgewater, NJ.


JAMA. 2001;286(17):2128-2135. doi:10.1001/jama.286.17.2128.
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Context Small-area variations in surgical rates raise concerns about access to care, treatment appropriateness, and the quality and cost of care.

Objective To measure small-area variations in rates of myringotomy with insertion of tympanostomy tubes (TTs) and to identify determinants of rate variation.

Design and Setting Retrospective analyses using hospital discharge data for patients who had undergone a myringotomy with insertion of TT by county in Ontario between April 1, 1996, and March 31, 1999. Information on possible determinants was taken from a survey of otolaryngologists and primary care physicians in 1996 and from the 1996 Canadian census and physician demographic databases for 1996-1999.

Participants A total of 75 358 hospitalizations for TT placement of children and adolescents (aged ≤14 years).

Main Outcome Measure Small-area variation in rates of TT.

Results An almost 10-fold difference between the areas with the highest and lowest rates was found (extremal quotient, 9.6; 95% confidence interval [CI], 8.2-11.1; P<.001). Higher rates occurred in counties with higher percentages of high school graduates (parameter estimate, 0.01; 95% CI, 0-0.02; P = .049); and where referring physicians were more likely to be male (parameter estimate, 0.01; 95% CI, 0-0.02; P = .01), North American–trained (parameter estimate, 0.01; 95% CI, 0.01-0.02; P<.001), and have higher propensities to refer for surgery (parameter estimate, 0.40; 95% CI, 0.09-0.72; P = .02). Otolaryngologist opinion was not a significant predictor.

Conclusion Substantial area variation in TT rates was observed. The opinion of primary care physicians was the dominant modifiable determinant, suggesting an area of research that may be important in reducing area variation in TT procedures.

Figures in this Article

Otitis media is a common childhood condition, affecting 65% to 93% of children by age 7 years.1 Myringotomy with the insertion of tympanostomy tubes (TTs) is the most common type of pediatric surgical procedure—more than 1 million operations are performed in the United States and Canada every year2,3—and may become more important given concerns about antibiotic-resistant bacteria.4

For many surgical procedures, the probability of having surgery depends on where one lives, a phenomenon termed small-area variation.5 The implication of variation in rates, which cannot be explained by differences in disease prevalence, is that patients in low-use areas may be receiving too little care or patients in high-use areas may be receiving too much (or inappropriate) care. Furthermore, due to the high prevalence of otitis media, variations in its treatment have implications for cost. Estimated direct and indirect costs of treatment in the United States exceed $5 billion a year.2 In Canada, with approximately one-tenth the population of the United States, the estimate is $611 million dollars6 (in 1994, the exchange rate was $1.00 [Canada] to $0.75 [United States]).

Area variation has been theorized to stem from differences in community population characteristics and methods of health care delivery, including the number, type, and opinions of medical practitioners.7 One goal of area variation research is "to identify sources of variation whose modification is both practical and desirable."8 The purpose of this study was to acquire important descriptive information to measure and explain variations in TT rates in Ontario.

Calculation of TT Rates

In Ontario, hospitals are required to report all inpatient and same-day surgical procedures. Such procedures account for over 96% of all TT operations (the remainder are performed in private offices).9 Universal public health insurance covers all medically necessary services; supplementary private insurance for these services is prohibited. Therefore, surgery is available to all on equal financial terms, unlike in the United Kingdom, where surgery may be performed outside the National Health Service, or in the United States, where lack of insurance may limit use.10

We searched hospital discharge records for fiscal years (April 1 through March 31) 1996 through 1999 for all children and adolescents (aged ≤14 years), accounting for 87.5% of all TT hospitalizations, who had undergone a myringotomy with insertion of TT (Canadian Classification of Diagnostic, Therapeutic and Surgical Procedures code 32.01). Records were excluded if the patient's place of residence could not be identified (0.5%) or if a valid patient identifier was not available, preventing linkage over time (1.2%).

Since hospitals vary in their coding protocols, our analysis focused on hospitalizations rather than procedures. (Some hospitals reported 2 TT procedure codes when a bilateral TT was performed, other institutions submitted a single procedure code.) Over the study period, 75 358 TT hospitalizations were identified.

The rate of TT hospitalizations was determined for each of the 49 counties in Ontario. Rate was defined as the number of TT hospitalizations for all children and adolescents in the county, irrespective of where these hospitalizations took place, divided by the resident population aged 14 years or younger. County populations were determined from the 1996 Canadian census. Direct standardization was used to adjust crude rates for differences in age and sex distributions among the counties. All analyses were performed on the standardized rates.

Quantification of Small-Area Variation

Potential overestimates of area variation occur if the population is small and rates of intervention are low.11 The common occurrence of TT surgery and the pooling of 4 years of data lessen the importance of these effects. Nonetheless, for robustness and comparability, we used 3 measures of variation: the extremal quotient (EQ), the weighted coefficient of variation (CV), and the systematic component of variance (SCV).11,12 The EQ is the ratio of the highest county TT rate to the lowest rate. The CV measures the ratio of the SD of 49 county TT rates to the mean rate, weighted by the population in each county to account for their unequal sizes, multiplied by 100. The SCV measures variations in rates after adjusting for random variations, and was multiplied by 1000. Measures of area variations in the literature refer to counts of events rather than to individuals, which has been followed here to permit comparisons.

The EQ is perhaps the most widely reported measure of area variation, and the easiest to understand. The drawback is that it depends only on the 2 most extreme rates, both of which may be outliers. The lowest rate, in particular, is likely to be sensitive to random variation and errors in the data. The CV is based on rates in all areas, but may overestimate variations when rates are low or when the area population is small.11 The SCV, developed to address these concerns, removes the component of variation attributed to population size, and provides a measure of variation that is stable across a range of rates and population sizes.11

Large variations in TT rates might occur by chance due to random fluctuation. To address this, we conducted a computer simulation12 using the observed distribution of TT hospitalizations per person over the study period. We determined how many children and adolescents had no TT procedures, how many had 1 TT procedure, how many had 2 TT procedures, etc, over 4 years. The resulting population was randomly assigned to the 49 counties, with each receiving the appropriate number of simulated children. This reflects the distribution of TT rates expected due to chance, under the null hypothesis of no differences among the counties. Summary measures of area variation (EQ, CV, and SCV) were computed for the simulated population. This was repeated 10 000 times so that tests could be conducted to determine whether our observed measures of variation were due to chance alone.

χ2 Tests were also used to test for variation in TT rates.12 Individual county rates were compared with the rate for the province as a whole, using a level of significance of .001 to adjust for multiple comparisons. χ2 Values were further adjusted using a multiple admissions factor to correct for the occurrence of multiple hospitalizations for some patients.12

Determination of Physician Characteristics

In Ontario, family physicians, general practitioners, and pediatricians (referring physicians) serve as the "gatekeepers" to the health care system. Patients can obtain consultations with specialists, such as otolaryngologists, generally only through a physician referral. We hypothesized that the characteristics and opinions of both otolaryngologists and referring physicians would affect rates.

The median age and median year of licensing of referring physicians and the percentage of women physicians and percentage of physicians who graduated from North American (Canada or United States) medical schools vs non–North American medical schools in each county in Ontario were obtained from the National Physician Demographic Databases for 1996 through 1999.

Referring physician opinions regarding TTs were obtained from a survey of all pediatricians in Ontario and a random sample of general practitioners/family physicians, mailed in the fall of 1996.13 The response rate was 52.5% for family physicians and 55.3% for pediatricians. Respondents tended to be younger, female, to have been trained in Canada, and to have been licensed more recently. These physician characteristics were not related to either the propensity to refer or opinions expressed about the outcomes.

It has been suggested that physician enthusiasm is the most important determinant of small-area variation.14 Two measures of physician enthusiasm were created. Survey respondents indicated, in 5 categories ranging from much less likely to much more likely to refer, the manner in which each of 17 clinical and social factors influenced their decision to refer a child for consideration of TT surgery. The first measure of physician enthusiasm, which we called propensity to refer,15 was based on each physician's enthusiasm for TT surgery, relative to his/her peers. (For example, most referring physicians indicated that they were more likely or much more likely to refer a child who showed no response to antibiotics or had >7 episodes of otitis media in 6 months. A physician who said these factors had no effect on the decision to refer would be said to show a low propensity to refer vis-à-vis these 2 items. The difference between an individual physician's response and the median response was calculated and summed over all 17 items to yield that physician's propensity to refer.) The propensity for TT surgery within a county was the sum of the propensities of all referring physicians within the county, adjusted for the survey sampling scheme, and weighted by the number of children or adolescents with otitis media seen in their practice.

A second measure of physician enthusiasm, which we termed outcome perceptions,15 was based on physicians' estimates of the proportion of children or adolescents who would have 9 different surgical outcomes, such as fewer episodes of acute otitis media, otorrhea, and need for tube reinsertion. Responses were combined in a fashion similar to the propensity score to create a single county-specific variable.

The survey also assessed the threshold at which a physician would refer a child for number of acute otitis media episodes over 6 months; number of months with middle ear effusion; level of bilateral conductive average pure tone hearing loss; and duration of antibiotic therapy without clinical improvements. Responses to these questions were combined to create a measure of the physician's threshold for referral.

The opinions of otolaryngologists were evaluated using data from a similar mail survey of all practicing otolaryngologists in Ontario.16 The response rate was 68.3%. Respondents tended to be younger than nonrespondents. Otolaryngologists' propensity to perform surgery was calculated in the manner described above and weighted averages were obtained based on the county in which the otolaryngologists practiced. Some counties in Ontario do not have any practicing otolaryngologists; children and adolescents in these counties received treatment in another county or in several other counties. The otolaryngologist propensity score for a given county was therefore based on the location of treatment. If 45% of the residents of county A were treated in county A, and 55% were treated in county B, then the otolaryngologist propensity score for county A was defined as (0.45 [propensity A] + 0.55 [propensity B]), in which propensity A is the propensity score reported by otolaryngologists from county A. County-level otolaryngologist scores for outcome perceptions and thresholds for performing surgery were calculated in the same way. Details of the calculations have been described elsewhere.15

Two measures of access to surgery were used. The number of referring physicians per 100 000 population was calculated as the sum of the number of family and general practitioners per 100 000 population plus the number of pediatricians per 100 000 population aged 14 years or younger. The number of specialists per 100 000 population was based on the number of otolaryngologists serving each county. If the otolaryngologists in county A performed all of the TTs for residents of county A and 50% of the TTs for residents of county B, then the number of otolaryngologists per 100 000 population in county A was calculated as: No. of otolaryngologists practicing in county A divided by (population of county A + 0.50 × population of county B). A county with no otolaryngologists was assigned a weighted average of the number of otolaryngologists per 100 000 population practicing in the counties in which its residents received their surgery.

Population Characteristics

County population was characterized using information from the 1996 census. We used the proportion of the population aged 14 years or younger and 2 socioeconomic measures: the proportion of households with an income under the low income cutoff (a measure of poverty developed by Statistics Canada based on the proportion of household income spent on food, clothing, and shelter); and the proportion of the population (aged ≥15 years) with at least a high school education. Finally, each county was classified as urban or rural based on its population density.

Number of hospital beds, generally invoked to explain small-area variation, was not used in this analysis because most (94.4%) TT procedures are performed as same-day surgeries. Information on the availability of operating rooms was not available.

Bivariate correlations between TT rate and each of the explanatory variables and interrelationships among explanatory variables were determined with Spearman correlation coefficient or Wilcoxon rank sum tests (for the binary urban/rural variable). Stepwise multiple linear regression and all possible subset regressions were used to determine factors associated with county use rates. We tested for violations of regression assumptions and used influence diagnostics to check for observations with undue influence on the regression results.17

Statistical analyses were performed using SAS statistical software.18 All P values were 2-tailed. The study was approved by the University of Toronto Ethics Review Committee.

Figure 1 depicts TT rates for children and adolscents in Ontario between 1996 and 1999. The overall rate was 8.35 per 1000 population aged 14 years or younger. The rate for males was more than 50% greater than that for females, 10.0 vs 6.6 per 1000. Rates were bimodal, peaking for children aged 1 year (20.4) and 4 years (16.3). This age-sex distribution is congruent with those reported for children and adolescents elsewhere in North America.19

Figure 1. Age- and Sex-Specific Tympanostomy Tube Rates in Ontario, 1996-1999
Graphic Jump Location

Figure 2 depicts the age-sex standardized TT rates for the 49 counties. χ2 Tests, adjusted for multiple TT insertions, were used to assign each county to 1 of 3 categories based on their rates relative to that for the province as a whole. Twelve predominantly rural areas, with 25.3% of the provincial population aged 14 years or younger, were significantly (P<.001) above the provincial TT rate of 8.35. In contrast, 6 mainly urban counties, with 42.7% of the provincial population, were significantly (P<.001) below the provincial rate. The remaining counties, with rates ranging from 3.83 to 11.97 per 1000 population, were not significantly different from the provincial average.

Figure 2. Variation in County Tympanostomy Tube (TT) Rates
Graphic Jump Location
Dotted line indicates TT rate equal to the overall provincial rate (8.35/1000).

Over the study period, the EQ was 9.6 (95% confidence interval, 8.2-11.1; P<.001); the maximum EQ expected by chance alone12 was 2.2. This implies almost a 10-fold difference in TT rates between extremal counties, even after adjusting for the age-sex composition of the population and pooling 4 years of data. The CV of 37.2 and the SCV of 267.9 were also significantly larger than can be explained by chance (P<.001). These results are consistent with the contention that there were large area variations in the surgical management of childhood otitis media in Ontario. Table 1 reports the results, with context provided by measures of rate variation for other common procedures and conditions.

Table Graphic Jump LocationTable 1. Small-Area Variation in Age- and Sex-Standardized Hospital Rates for Tympanostomy Tube Insertion and Other Various Procedures and Conditions in Ontario*

County characteristics are presented in Table 2. Missing values for some counties are due primarily to lack of survey responses from counties with small numbers of specialists. A wide range of values are reported for propensity to perform (or refer for) TT, thresholds for surgery, and outcome perceptions among otolaryngologists and referring physicians, as well as for a range of physician and population characteristics. Weak bivariate correlations between referring physician opinion and TT rates were observed, with higher rates associated with a higher propensity to refer for surgical consideration and a lower threshold for referral. Place of training was also weakly correlated with TT rates—counties with a greater proportion of referring physicians trained in North America tended to have higher rates.

Table Graphic Jump LocationTable 2. Relationship Between the Characteristics of Counties in Ontario and Tympanostomy Tube Rates

Rates of TT showed stronger bivariate correlations with otolaryngologists' opinions, particularly their propensity to perform the procedure and the threshold at which they felt surgery was appropriate. Proportion of female specialists in the county was the strongest single predictor of TT rates, with higher rates in counties having relatively few female otolaryngologists.

The results of the multivariable models, using a number of different multiple linear-regression techniques, consistently identified the same significant predictors of TT rates. Higher rates were associated with counties with relatively more North American-trained referring physicians, with more adults with at least a high school education, and with a higher propensity of county physicians to refer children or adolescents for TT surgery. Higher proportions of referring physicians who were female were associated with lower TT rates. Regression diagnostics identified 2 counties, both with high proportions of female physicians, 1 with the lowest rate of completed high school education and 1 with the highest rate, as having a large influence on the parameter estimates. Removing these 2 observations did not affect the choice of explanatory variables in the model. Table 3 reports the results of the regression after removing these 2 counties. The final model explains 34.2% of the total variation in TT rates. The standardized coefficients indicate that the proportion of physicians trained in North America is the strongest of the 4 predictors, followed by the proportion of female physicians. Given this model, which contains variables related to referring physician characteristics, none of the variables related to otolaryngologists contributed a significant amount of additional information. The reverse was not true. Given a model that contained the significant variables related to specialist characteristics, referring physician propensity was significant (P = .03), and proportion of female referring physicians was marginally significant (P = .08). It appeared that TT rates, at the county level, could be predicted without reference to the characteristics of otolaryngologists.

Table Graphic Jump LocationTable 3. Multivariable Regression Model for County Tympanostomy Tube (TT) Rate per 1000 Children and Adolescents*

As an aid to interpreting the variables included or excluded from the multivariable regression model, Table 4 presents correlations between those variables selected for the model and other explanatory variables. (Only correlations significant at the ≤.05 level are shown.) The variables that were included in the model are associated with availability of referring physicians, with referring physicians' threshold for referring a patient for surgical consideration, and with urban counties. Population education and referring physician place of training were also associated with the proportion of female otolaryngologists, explaining why this variable did not appear in the multivariable model.

Table Graphic Jump LocationTable 4. Associations Between Variables Included in the Regression Model and Other Potential Explanatory Variables*

Myringotomy with insertion of TTs is the most common surgical procedure performed on children and adolescents.2,3 Despite its frequency and cost,2,6 there is an absence of extensive epidemiological and health services research.1 Little is known about the magnitude and reasons for variations in TT rates.

The substantial TT rate variations reported in this study exceed those previously published for other jurisdictions20,21 and are larger than those reported for almost all other procedures,1,11,22 raising concerns about health system costs and treatment appropriateness. With such large regional variations, there may be some jurisdictions in which children and adolescents are not receiving the care they need and other regions where TT surgery may be performed unnecessarily.

The main intent of this study was to identify factors related to small-area variation that might be amenable to intervention.8 Rates of TT were higher in counties with relatively more primary care physicians trained in North America, and lower in counties with higher proportions of female primary care physicians. This may be related to practice patterns as well as training. Our survey found that female referring physicians are younger, more likely to work part-time, and to work in group practices, rather than solo practices (data not shown). The percentage of the population with a high school education (a socioeconomic variable) was also related to area variation, with higher rates in counties with a more educated population. This finding agrees with the results of other studies, which have found that socioeconomic status may explain a large proportion of rate variation.7,21

Counties with fewer female physicians and more North American–trained physicians tended to be rural. In contrast, higher levels of educational achievement tended to occur in urban counties. Thus, the bivariate relationships between rural/urban location and TT rates appear to be related to physician characteristics modified by educational achievement. The rural/urban variable was not a significant predictor in the multivariable regression model.

Some studies have found that physician density is related to area variation.7,23 However, we found no relationship between density of either referring physicians or otolaryngologists and use rates. Thus, attempts to change the distribution of surgeons may have little effect on variation in the use of TT surgery. This finding agrees with an earlier study that found no relationship between rates of total knee replacements and physician density in Ontario.24

The 1 factor related to area variation in this study that is potentially amenable to intervention was physician opinion. We found that the referring physician's opinion or enthusiasm for TTs was an important determinant of rate variations, with higher TT rates associated with greater propensity to refer. Although reduction in variation in the opinions of physicians has the potential to reduce small-area variation, this does not ensure that the "right" rate will be achieved.25 However, while clinicians will always vary somewhat in their enthusiasm for a procedure, if variation in physicians' opinions represents uncertainty or misperceptions about the risks and benefits of surgery, addressing opinions that do not match published literature and evidence-based practice guidelines provides one of the best opportunities to reduce rate variation.

This study found that it was the opinion of primary care physicians that predicted rates. This contrasts with the results of an earlier study that found that the opinions of surgeons, rather than of referring physicians, predicted rates of total knee replacements.15 The survey results13,16 suggest that by the time children or adolescents meet the referring physicians' criteria for referral for TTs, they may meet or exceed the criteria of the otolaryngologist to perform the procedure. Our results suggest that efforts to reduce uncertainty among physicians be directed at primary care providers.

There are 2 main study limitations. The first is lack of data about the prevalence or severity of otitis media in different counties. Health services literature has shown that while the prevalence of disease may be associated with area variation in procedure rates, it is not generally the dominant factor.5,19 The second is that we did not have information about parents' preferences for the treatment of their children. For many surgical procedures, patients' preferences (or the preferences of their parents) are an important determinant of decision making.26,27 Accounting for parental preferences may explain at least part of the observed variation.27 However, parental preferences may be partially based on information received from clinicians about the risks and benefits of a procedure. If clinicians are providing variable (or inaccurate) information, this may lead to misperceptions and ill-informed decision making.

A further limitation is that the study was based on hospital discharge data acquired from the Canadian Institute for Health Information. The main methodological concern with the use of administrative data is the validity and reliability of the data.28,29 Studies that have compared administrative data with hospital chart data have overwhelmingly concluded that major events, such as surgical procedures and mortality, patient demographics, and primary diagnosis are coded accurately.29 As well, number of children and adolescents with otitis media seen in the previous month (the variable used to weight physician opinions) was based on recall and is subject to memory biases.

Our study was confined to clinical practice in Ontario for the period 1996 to 1999. The results will not necessarily generalize to other jurisdictions, even within Canada, nor to other periods in Ontario. However, they are worth consideration in any system in which primary care physicians play an important role in gatekeeping, or have the opportunity to counsel patients with respect to treatment and referral.

In conclusion, substantial variations in age-sex standardized TT rates were observed in Ontario. These variations were exceptionally large compared with TT rate variations in other jurisdictions, and compared with rate variations for other medical and surgical procedures. After controlling for population characteristics and access to care, the enthusiasm of referring physicians for this procedure was the dominant modifiable determinant of area variation. Providing referring physicians with evidence-based guidelines addressing areas of uncertainty they face in managing children and adolescents with otitis media may help to reduce variation. Future research will be necessary to determine how patient characteristics should affect the decision to refer and how they affect the actual surgical outcomes. Furthermore, we need to determine the reasons for differences in the opinions of the gatekeepers to classify these reasons into exogenous and modifiable factors, and finally, test strategies to reduce variation in their opinions.25

Infante-Rivard C, Fernandez A. Otitis media in children: frequency, risk factors and research avenues.  Epidemiol Rev.1993;15:444-465.
Gates GA. Cost-effectiveness considerations in otitis media treatment.  Otolaryngol Head Neck Surg.1996;114:525-530.
To T, Coyte PC, Feldman W, Dick PT, Tran M. Myringotomy with insertion of ventilation tubes. In: Goel V, Williams JI, Anderson GM, Blackstien-Hirsch P, Fooks C, Naylor CD, eds. Patterns of Health Care in Ontario: The ICES Practice Atlas. 2nd ed. Ottawa, Ontario: Canadian Medical Association; 1996:297-300.
Berman S. Otitis media in children.  N Engl J Med.1995;332:1560-1565.
Wennberg J, Gittlesohn A. Variations in medical care among small areas.  Sci Am.1982;246:120-134.
Coyte PC, Asche CV, Elden LM. The economic cost of otitis media in Canada.  Int J Pediatr Otorhinolaryngol.1999;49:27-36.
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;12:741-808.
Blumenthal D. The variation phenomenon in 1994.  N Engl J Med.1994;331:1017-1018.
Ontario Ministry of Health.  Ontario Health Insurance Plan Detailed Claims File April 1, 1991 to March 31, 1996. Toronto: Ontario Ministry of Health; 1996.
Flood CM, Archibald T. The illegality of private health care in Canada.  CMAJ.2001;164:825-830.
McPherson K, Wennberg JE, Hovind OB, Clifford P. Small-area variations in the use of common surgical procedures: an international comparison of New England, England, and Norway.  N Engl J Med.1982;307:1310-1314.
Diehr P, Cain KC, Kreuter W, Rosenkranz S. Can small-area analysis detect variation in surgery rates?  Med Care.1992;30:484-502.
McIsaac WJ, Coyte P, Croxford R, Harji S, Feldman W. Referral of children with otitis media: do family physicians and pediatricians agree?  Can Fam Physician.2000;46:1780-1788.
Chassin MR. Explaining geographic variations: the enthusiasm hypothesis.  Med Care.1993;31:YS37-YS44.
Wright JG, Hawker GA, Bombardier C.  et al.  Physician enthusiasm as an explanation for area variation in the utilization of knee replacement surgery.  Med Care.1999;37:946-956.
McIsaac WJ, Coyte PC, Croxford R, Asche CV, Friedberg J, Feldman W. Otolaryngologists' perceptions of the indications for tympanostomy tube insertion in children.  CMAJ.2000;162:1285-1288.
Fox J. Regression diagnostics: an introduction. In: Sage University Paper Series on Quantitative Applications in the Social Sciences, Serices No. 07-079. Newbury Park, Calif: Sage; 1991.
 SAS [computer program]. Version 8. Cary, NC: SAS Institute Inc; 1999.
Bright RA, Moore RM, Jeng LL.  et al.  The prevalence of tympanostomy tubes in children in the United States, 1988.  Am J Public Health.1993;83:1026-1028.
Pedersen CB, Olsen J. Danish approach to the treatment of secretory otitis media: report of the Danish Consensus Conference, Copenhagen 1987.  Ann Otol Rhinol Laryngol.1990;99(suppl 146):1-28.
Bisset AF, Russell D. Grommets, tonsillectomies, and deprivation in Scotland.  BMJ.1994;308:1129-1132.
Goel V, Anderson G, Williams JI, Naylor CD. Patterns of Health Care in Ontario. Ottawa, Ontario: Canadian Medical Association; 1996.
Folland S, Stano M. Small area variations: a critical review of propositions, methods, and evidence.  Med Care Rev.1990;47:419-465.
Coyte PC, Hawker G, Wright JG. Variations in knee replacement utilization rates and the supply of health professionals in Ontario, Canada.  J Rheumatol.1996;23:1214-1220.
Grad R, Tamblyn R, McLeod PJ, Snell L, Illescas A, Boudreau D. Does knowledge of drug prescribing predict drug management of standardized patients in office practice?  Med Educ.1997;31:132-137.
Barry MJ, Fowler FJJ, Mulley Jr AG, Henderson Jr JV, Wennberg JE. Patient reactions to a program designed to facilitate patient participation in treatment decisions for benign prostatic hyperplasia.  Med Care.1995;33:771-782.
Hawker GA, Wright JG, Coyte PC.  et al.  Determining the need for hip and knee arthroplasty: the role of clinical severity and patients' preferences.  Med Care.2001;39:206-216.
Hsia DC, Krusnat WM, Fagan AB, Tebbutt JA, Kusserow RP. Accuracy of diagnostic coding for Medicare patients under the prospective payment system.  N Engl J Med.1988;318:352-355.
Hawker GA, Coyte PC, Paul JE, Wright JG, Bombardier C. Accuracy of administrative claims data in assessing patient characteristics and course in hospital for knee replacement surgery.  J Clin Epidemiol.1997;50:265-273.

Figures

Figure 1. Age- and Sex-Specific Tympanostomy Tube Rates in Ontario, 1996-1999
Graphic Jump Location
Figure 2. Variation in County Tympanostomy Tube (TT) Rates
Graphic Jump Location
Dotted line indicates TT rate equal to the overall provincial rate (8.35/1000).

Tables

Table Graphic Jump LocationTable 1. Small-Area Variation in Age- and Sex-Standardized Hospital Rates for Tympanostomy Tube Insertion and Other Various Procedures and Conditions in Ontario*
Table Graphic Jump LocationTable 2. Relationship Between the Characteristics of Counties in Ontario and Tympanostomy Tube Rates
Table Graphic Jump LocationTable 3. Multivariable Regression Model for County Tympanostomy Tube (TT) Rate per 1000 Children and Adolescents*
Table Graphic Jump LocationTable 4. Associations Between Variables Included in the Regression Model and Other Potential Explanatory Variables*

References

Infante-Rivard C, Fernandez A. Otitis media in children: frequency, risk factors and research avenues.  Epidemiol Rev.1993;15:444-465.
Gates GA. Cost-effectiveness considerations in otitis media treatment.  Otolaryngol Head Neck Surg.1996;114:525-530.
To T, Coyte PC, Feldman W, Dick PT, Tran M. Myringotomy with insertion of ventilation tubes. In: Goel V, Williams JI, Anderson GM, Blackstien-Hirsch P, Fooks C, Naylor CD, eds. Patterns of Health Care in Ontario: The ICES Practice Atlas. 2nd ed. Ottawa, Ontario: Canadian Medical Association; 1996:297-300.
Berman S. Otitis media in children.  N Engl J Med.1995;332:1560-1565.
Wennberg J, Gittlesohn A. Variations in medical care among small areas.  Sci Am.1982;246:120-134.
Coyte PC, Asche CV, Elden LM. The economic cost of otitis media in Canada.  Int J Pediatr Otorhinolaryngol.1999;49:27-36.
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;12:741-808.
Blumenthal D. The variation phenomenon in 1994.  N Engl J Med.1994;331:1017-1018.
Ontario Ministry of Health.  Ontario Health Insurance Plan Detailed Claims File April 1, 1991 to March 31, 1996. Toronto: Ontario Ministry of Health; 1996.
Flood CM, Archibald T. The illegality of private health care in Canada.  CMAJ.2001;164:825-830.
McPherson K, Wennberg JE, Hovind OB, Clifford P. Small-area variations in the use of common surgical procedures: an international comparison of New England, England, and Norway.  N Engl J Med.1982;307:1310-1314.
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