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Colin B. Begg, PhD; Laura D. Cramer, ScM; William J. Hoskins, MD; Murray F. Brennan, MD

JAMA. 1998;280:1747-1751.

ABSTRACT
Context.— Hospitals that treat a relatively high volume of patients for selected surgical oncology procedures report lower surgical in-hospital mortality rates than hospitals with a low volume of the procedures, but the reports do not take into account length of stay or adjust for case mix.

Objective.— To determine whether hospital volume was inversely associated with 30-day operative mortality, after adjusting for case mix.

Design and Setting.— Retrospective cohort study using the Surveillance, Epidemiology, and End Results (SEER)–Medicare linked database in which the hypothesis was prospectively specified. Surgeons determined in advance the surgical oncology procedures for which the experience of treating a larger volume of patients was most likely to lead to the knowledge or technical expertise that might offset surgical fatalities.

Patients.— All 5013 patients in the SEER registry aged 65 years or older at cancer diagnosis who underwent pancreatectomy, esophagectomy, pneumonectomy, liver resection, or pelvic exenteration, using incident cancers of the pancreas, esophagus, lung, colon, and rectum, and various genitourinary cancers diagnosed between 1984 and 1993.

Main Outcome Measure.— Thirty-day mortality in relation to procedure volume, adjusted for comorbidity, patient age, and cancer stage.

Results.— Higher volume was linked with lower mortality for pancreatectomy (P=.004), esophagectomy (P<.001), liver resection (P=.04), and pelvic exenteration (P=.04), but not for pneumonectomy (P=.32). The most striking results were for esophagectomy, for which the operative mortality rose to 17.3% in low-volume hospitals, compared with 3.4% in high-volume hospitals, and for pancreatectomy, for which the corresponding rates were 12.9% vs 5.8%. Adjustments for case mix and other patient factors did not change the finding that low volume was strongly associated with excess mortality.

Conclusions.— These data support the hypothesis that when complex surgical oncologic procedures are provided by surgical teams in hospitals with specialty expertise, mortality rates are lower.

INTRODUCTION

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A NUMBER of cancer studies have been conducted using hospital volume of patients treated as a measure of surgical expertise, following a tradition of the use of patient volume in studies of variations in outcomes between hospitals and between surgeons.¹ In the United States, all population-based studies of this issue have used state discharge databases and in-hospital mortality as the end point, notably the studies of pancreatectomy in New York,² California,³ and Maryland⁴; studies of lung cancer in California⁵; and hepatic resections in Maryland.⁶ All these studies demonstrated much lower mortality in high-volume hospitals.

There are significant limitations to the use of discharge data for this purpose. First, one must use in-hospital mortality as the end point, but this could be affected by hospital policies regarding length of stay. Case mix adjustments for disease severity are limited by the availability and quality of data on disease severity in the discharge database. Finally, one cannot effectively identify individual patients and link them to their cancer diagnosis for the purpose of creating a population-based cohort of incident cases and for determining important factors such as time since diagnosis.

In our study, we circumvented these problems by accessing the Surveillance, Epidemiology, and End Results (SEER)–Medicare linked database.⁷ Use of the SEER database permitted the creation of a population-based census of incident cancer patients during the target time period for the study (1984-1993). Linkage to Medicare permitted, for patients older than 65 years, identification of precise details of the surgical procedures performed, if any, including dates, information on comorbidities, and follow-up data on survival. The most critical attribute of this approach is the ability to determine survival at a landmark time point, 30 days after surgery, thereby eliminating the need to use the potentially biased discharge status in evaluating mortality rates.

To our knowledge, the only study that has evaluated postoperative 30-day mortality in a similar population-based fashion is the study of colorectal cancer surgery in Scotland,⁸ in which variations in mortality rates among surgeons were observed, although there was no apparent effect of surgeon volume.

METHODS

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Selection of Study Hypotheses

In studying a general hypothesis using a large database with information on all cancers, there is a danger of overinterpreting apparent correlations due to the many sites and procedures that could be studied and the various ways that mortality and volume could be defined. Thus, we approached this study in a hypothesis-driven fashion by developing a protocol and specifying in advance the precise details of our methodology, including the cancer sites and procedures to be studied, the measures of volume and mortality to be used, and the statistical tests to be used. This protocol was reviewed and approved by representatives from the National Cancer Institute (SEER) and the Health Care Financing Administration (Medicare) primarily to address issues of confidentiality and feasibility. After this approval, we were given access only to data for the sites of disease specified in our protocol. The analysis and interpretation of the data are the sole responsibility of the authors and do not represent the views of either the National Cancer Institute or Health Care Financing Administration.

Specific Procedures Studied and Rationale

Experienced surgeons at our institution determined on the basis of collective knowledge the procedures that they believed to be sufficiently complex that mortality differences should be detectable between high-volume and low-volume hospitals. Five procedures were selected: pancreatectomy, including proximal pancreatectomy (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] code 52.51), radical subtotal pancreatectomy (ICD-9-CM 52.53), other partial pancreatectomy (ICD-9-CM 52.59), total pancreatectomy (ICD-9-CM 52.6), and radical pancreaticoduodenectomy (ICD-9-CM 52.7); esophagectomy, including esophagectomy not otherwise specified (ICD-9-CM 42.40), partial esophagectomy (ICD-9-CM 42.41), and total esophagectomy (ICD-9-CM 42.42); complete pneumonectomy (ICD-9-CM 32.5); hepatic resection, including partial hepatectomy (ICD-9-CM 50.22), and lobectomy of liver (ICD-9-CM 50.3); pelvic exenteration, including radical cystectomy (ICD-9-CM 57.71); and pelvic evisceration (ICD-9-CM 68.8). In general, these procedures involve preoperative judgment, diagnostic accuracy, meticulous surgical technique, and demanding postoperative care. Thus, they are all major procedures with significant risk of serious postoperative morbidity and mortality.

SEER-Medicare Linked Database

The SEER database consists of all incident cases of cancer in several defined geographic populations comprising approximately 10% of the population of the United States.⁹ The Medicare database has information on all Medicare claims, and it encompasses 97% of individuals aged 65 years or older. The Medicare Provider Analysis and Review files contain records on 100% of hospital admissions since 1984.⁷ Up to 5 diagnoses and up to 3 procedures were coded using the ICD-9-CM between 1984 and 1991, with a subsequent increase in the number of codes available. This file also contains dates of the procedures and the date of death. Investigators at the National Cancer Institute and the Health Care Financing Administration have succeeded in matching 94% of the SEER cases with their Medicare records.⁷

Data

Potential study subjects comprised incident cases of the cancers that made them candidates for 1 of the 5 following procedures: pancreatectomy, cancer of the pancreas (ICD-9-CM 157); esophagectomy, cancer of the esophagus (ICD-9-CM 150); pneumonectomy, cancer of the lung or bronchus (ICD-9-CM 162.2-9); hepatic resection, liver metastases following cancers of the colon and rectum (ICD-9-CM 153, 154.0, 154.1, 154.8); or pelvic exenteration for cancers of the cervix, endometrium, bladder, colon, and rectum (ICD-9-CM 153, 154, 173.5, 179, 180, 182, 184.0-2, 184.4-9, 188, 195.3). The study included all cases incident in the SEER registry between 1984 and 1993, inclusive. Our protocol specified that the patient be included in the analysis only if the designated procedure was performed within 2 months of diagnosis, to limit patient heterogeneity, except for hepatic resection, for which the number of procedures at the time of incidence was inadequate for meaningful analysis. Mortality was defined as death within 30 days of hospitalization. We used the date of hospitalization as a replacement for the date of surgery, since the former is coded more reliably in the Medicare database.

Validity of Volume Measure

Hospitals were classified by volume on the basis of the total number of procedures performed in this study between 1984 and 1993. Since the study was restricted to patients 65 years or older, we were concerned that our measure of volume might not accurately reflect experience with the procedure because many procedures would be performed in the hospitals in younger patients and in patients who were not diagnosed as having cancer. To evaluate the validity of our measure of volume, we examined data from the New York State discharge database. We identified all hospitals at which the index procedure had been performed at least 6 times between the years 1990 and 1995 in cancer patients 65 years or older. We ranked these hospitals according to the number of procedures performed in patients 65 years or older and also according to the total number of procedures across all ages. The rank correlations of these 2 rankings are presented in Table 1, using the Kendall rank statistic.¹⁰ The high values of these correlations support the use of volume as calculated in our study as a valid measure of the ranking of hospitals based on the total volume of procedures conducted.

View this table: [in this window] [in a new window] Table 1.—Validation Study Using New York State Discharge Database*

Statistical Analysis and Power

Our protocol specified that we would assess the impact of volume on mortality using the Mantel-Haenszel test for trend.¹¹ We elected to perform this analysis without any aggregation to maximize power and eliminate the opportunity to select cut points to optimize the P values. However, in our graphs we display mortality rates in 3 aggregated volume groupings for visual effect. Confidence intervals (CIs) are 95% exact intervals for binomial proportions. Our protocol did not specify precisely how we would accomplish adjustments for case mix. After evaluating the availability and quality of the data, we elected to use a modified comorbidity index. Our index is the one proposed by Romano et al,¹² with the contributions "any malignancy" and "metastatic solid tumor" eliminated. A validation study of this index was conducted by Ghali et al.¹³ The index is a modification of the one originally proposed by Charlson et al¹⁴ and it comprises a weighted sum of designated comorbid illnesses. We also adjusted for patient age, grouped into 3 categories (ages 65-69, 70-74, and 75 years). In addition, our linkage to the SEER database allowed us to evaluate the influence of the extent of disease by adjusting for cancer stage. The impact of volume on mortality was adjusted for these factors using logistic regression in which the outcome of the patient was that he/she was alive or dead at 30 days, volume was entered as a continuous variable, and comorbidity, cancer stage, and age were classified using indicator variables for the categories in Table 4, Table 5, and Table 6. The power of the study was projected in the protocol based on results of earlier studies of pancreatectomy and lung cancer in the literature and a 2-sided test at the 5% significance level. These projections indicated high power, in excess of 95%. Power was not estimated for the remaining procedures due to lack of available data to make meaningful projections.

View this table: [in this window] [in a new window] Table 4.—Volume by Comorbidity

View this table: [in this window] [in a new window] Table 5.—Volume by Stage

View this table: [in this window] [in a new window] Table 6.—Volume by Age

RESULTS

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Accrual of incident cases into the study is described in Table 2. The data show that a relatively small percentage of elderly patients with these cancers are candidates for these highly invasive procedures. For example, among the 19,205 incident cases of cancer of the pancreas in SEER, diagnosed at age 65 years or older between 1984 and 1993, only 742 patients (3.9%) underwent a pancreatectomy within 2 months of having been diagnosed as having cancer. These percentages are somewhat higher but still relatively low when we restrict attention to patients with localized or regional disease.

View this table: [in this window] [in a new window] Table 2.—Patient Selection Statistics

The 30-day mortality rates are presented by volume in Table 3. Thus, for pancreatectomy, the first entry presents combined results for the 126 hospitals, each of which performed 1 pancreatectomy, resulting in an average 30-day mortality rate of 14% (18/126). Statistical analysis for a trend of decreasing mortality with increasing volume leads to P=.004 for pancreatectomy, P<.001 for esophagectomy, P=.32 for pneumonectomy, P=.04 for hepatic resection, and P=.04 for pelvic exenteration. The precise nature of the trends are observed more clearly in the Figure 1, in which the volume categories have been aggregated.

View this table: [in this window] [in a new window] Table 3.—Mortality Rates by Hospital Volume

View larger version (37K): [in this window] [in a new window] The points on the graphs represent 30-day mortality rates, aggregated across the designated volume categories. Error bars represent 95% confidence intervals.

The potential impact of case mix on these results is displayed in Table 4, Table 5, and Table 6. In Table 4, the aggregated volume categories are cross-tabulated with the comorbidity index. In general, the distribution of comorbidity is not strongly related to volume, although this association is significant for pancreatectomy (P=.04). No evidence of appreciable patient selectivity on the basis of cancer stage (Table 5) or patient age (Table 6) exists, with the exception that low-volume institutions more frequently report the patient to SEER as unstaged. The relatively small percentages of cases with metastatic disease were presumably restaged as such because of distant spread discovered during the procedure. The P values for the effects of volume on mortality for each site, after adjusting for these factors using logistic regression, were as follows: pancreatectomy P=.01; esophagectomy P<.001; pneumonectomy P=.19; hepatic resection P=.05; pelvic exenteration P=.05. Thus, the results are essentially unaffected by the case mix adjustments. Finally, there was no evidence that discharge prior to death within 30 days had any influence on the results. This was a relatively rare occurrence, except for pneumonectomy, which was evenly distributed across volume categories.

COMMENT

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The data provide strong evidence that experience in performing these complex procedures, as represented by hospital volume, results in substantially lower operative mortality. The results are particularly striking for esophagectomy, for which the 30-day mortality drops from 17.3% (95% CI, 13.3%22.0%) in the lowest volume category to 3.4% (95% CI, 0.7%-9.6%) in the highest volume category. For the other sites the corresponding reductions were as follows: pancreatectomy, 12.9% (95% CI, 9.7%-16.6%) to 5.8% (95% CI, 2.5%-11.0%); pneumonectomy, 13.8% (95% CI, 10.9%-17.2%) to 10.7% (95% CI, 8.0%-14.0%); hepatic resection, 5.4% (95% CI, 3.6%-7.8%) to 1.7% (95% CI, 0.4%-5.0%); and pelvic exenteration, 3.7% (95% CI, 2.3%-5.5%) to 1.5% (95% CI, 0.7%-2.8%).

Clinically, these differences are understandable, since esophagectomy and pancreatectomy are procedures for which morbidity is high, and serious morbidity, such as fistula formation, commonly translates into mortality. In pneumonectomy and hepatectomy, the outcome is highly influenced by the intraoperative decision to proceed in a low-risk patient. This is highlighted by the fact that for hepatic resections the preponderance of procedures are less than lobar (69%). Removal of the pelvic viscera (pelvic exenteration) requires removal of the genital organs in combination with the bladder or rectum or both, followed by reconstruction and a diversion of the urinary and gastrointestinal tract. Most centers that perform these procedures in volume develop a 2-team approach in which one team performs the exenteration and the second team performs the reconstruction. Thus, effective coordination of the surgical staff members is important.

Our study demonstrates that these procedures are performed on relatively small proportions of patients with incident cancers, at least in the restricted age group under investigation. For example, our study indicates that only 3.9% of incident cases of pancreatic cancer undergo pancreatic resection within 2 months of diagnosis. Thus, the patients evaluated in our study constitute a highly selected group, and one can only speculate at the selection factors that play a role. Despite this, our evaluation of comorbidity appears to indicate little evidence that the high-volume hospitals are operating on a more favorable group of patients. The distributions of the comorbidity index as well as cancer stage and age are largely independent of hospital volume, and as a result, the statistical tests are unaffected by adjustments for these factors.

The representativeness of the SEER population and its providers for health care research of this nature is a topic that has received recent attention. Nattinger et al¹⁵ have compared the SEER catchment to the entire United States with respect to a variety of characteristics. Although some significant differences were observed, there was no significant difference in either the density of board-certified oncologists or of general surgical specialists. The most cogent issue regarding generalizability in our study is that the use of Medicare restricted our population to patients aged 65 years or older. It is likely that the overall surgical mortality rate should be lower in younger age groups. This is indicated, for example, for pancreatic cancer in 1 of the discharge database studies.² Despite the possible influence of age on mortality, it is certainly plausible, indeed likely, that the trend of lower mortality with increased volume may be unaffected by the age restriction in our study.

Our results are broadly consistent with the previous population-based studies of these procedures cited earlier,^2-6 although a multi-institutional study of pancreatectomy showed no volume effect¹⁶ and the large survey of pancreatic cancer conducted by the American College of Surgeons detected only a small volume trend.¹⁷ Variations between surgeons within individual hospitals favoring experienced surgeons have also been observed for pancreatectomy in studies by Pellegrini et al¹⁸ and Andren-Sandberg and Ihse.¹⁹ Related research in studies of breast cancer in the United Kingdom showed specialty care to be associated with long-term survival in 2 studies^20-21 and with quality-of-life outcomes in another.²² Finally, a large study of ovarian cancer demonstrated inferior long-term survival in patients treated by general surgeons compared with specialists.²³

In summary, our study contributes to the growing literature supporting the hypothesis that specialist cancer care significantly improves patient outcomes, with the caveat that we are using patient volume to represent specialization. When procedures such as pancreatectomy and esophagectomy are attempted, there is strong evidence that these can be performed more safely in high-volume referral centers. The data support a similar conclusion for hepatic resection and pelvic exenteration, although with less statistical conviction.

AUTHOR INFORMATION

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Support was provided by institutional research funds of the Memorial Sloan-Kettering Cancer Center.

The interpretation and reporting of these data are the sole responsibility of the authors.

We are extremely grateful for the advice and assistance of the following individuals: Mark Radzyner, Kathy Schleeter, and Joan Warren. The study used the Linked Medicare-Tumor Registry Database. We acknowledge the efforts of several groups responsible for creation and dissemination of the linked database, including the Applied Research Branch, Division of Cancer Prevention and Control, National Cancer Institute; the Office of Research and Demonstrations and the Bureau of Data Management and Strategy, Health Care Financing Administration; Information Management Services, Inc; and the Surveillance, Epidemiology, and End Results (SEER) Program tumor registries.

Corresponding author: Colin B. Begg, PhD, 1275 York Ave, Box 44, New York, NY 10021 (e-mail: beggc{at}mskcc.org).

From the Departments of Epidemiology and Biostatistics (Dr Begg and Ms Cramer) and Surgery (Drs Hoskins and Brennan), Memorial Sloan-Kettering Cancer Center, New York, NY.

REFERENCES

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On Referral Patterns for Patients With Breast Cancer
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JCO 2007;25:244-246.
FULL TEXT  

Volume-Based Referral for Cancer Surgery: Informing the Debate
Hollenbeck et al.
JCO 2007;25:91-96.
ABSTRACT | FULL TEXT  

Total Joint Arthroplasty: When Do Fatal or Near-Fatal Complications Occur?
Parvizi et al.
JBJS 2007;89:27-32.
ABSTRACT | FULL TEXT  

Surgeon and Hospital Characteristics as Predictors of Major Adverse Outcomes Following Colon Cancer Surgery: Understanding the Volume-Outcome Relationship
Billingsley et al.
Arch Surg 2007;142:23-31.
ABSTRACT | FULL TEXT  

Trends in lung surgery: United States 1988 to 2002.
Memtsoudis et al.
Chest 2006;130:1462-1470.
ABSTRACT | FULL TEXT  

Disparities in the utilization of high-volume hospitals for complex surgery.
Liu et al.
JAMA 2006;296:1973-1980.
ABSTRACT | FULL TEXT  

Surgical Mortality in Patients With Esophageal Cancer: Development and Validation of a Simple Risk Score
Steyerberg et al.
JCO 2006;24:4277-4284.
ABSTRACT | FULL TEXT  

Neoadjuvant chemoradiation may increase the risk of respiratory complications and sepsis after transthoracic esophagectomy
Reynolds et al.
J. Thorac. Cardiovasc. Surg. 2006;132:549-555.
ABSTRACT | FULL TEXT  

Hospital volume and the outcomes of mechanical ventilation.
Kahn et al.
NEJM 2006;355:41-50.
ABSTRACT | FULL TEXT  

Mitral repair best practice: proposed standards
Bridgewater et al.
Heart 2006;92:939-944.
ABSTRACT | FULL TEXT  

Outcomes and Health-Related Quality of Life After Esophagectomy for High-Grade Dysplasia and Intramucosal Cancer
Moraca and Low
Arch Surg 2006;141:545-551.
ABSTRACT | FULL TEXT  

Mortality After Major Surgery for Urologic Cancers in Specialized Urology Hospitals: Are They Any Better?
Konety et al.
JCO 2006;24:2006-2012.
ABSTRACT | FULL TEXT  

Transcending the Volume-Outcome Relationship in Cancer Care
Lipscomb
JNCI J Natl Cancer Inst 2006;98:151-154.
FULL TEXT  

Associations Between Hospital and Surgeon Procedure Volumes and Patient Outcomes After Ovarian Cancer Resection
Schrag et al.
JNCI J Natl Cancer Inst 2006;98:163-171.
ABSTRACT | FULL TEXT  

Impact of Hospital Volume on Racial Disparities in Cardiovascular Procedure Mortality
Trivedi et al.
J Am Coll Cardiol 2006;47:417-424.
ABSTRACT | FULL TEXT  

Hospital volume: operative morbidity, mortality and survival in thoracotomy for lung cancer.: A Spanish multicenter study of 2994 cases
Freixinet et al.
Eur. J. Cardiothorac. Surg. 2006;29:20-25.
ABSTRACT | FULL TEXT  

Annual Report to the Nation on the Status of Cancer, 1975-2002, Featuring Population-Based Trends in Cancer Treatment
Edwards et al.
JNCI J Natl Cancer Inst 2005;97:1407-1427.
ABSTRACT | FULL TEXT  

Population-Based Assessment of Surgical Treatment Trends for Patients With Melanoma in the Era of Sentinel Lymph Node Biopsy
Cormier et al.
JCO 2005;23:6054-6062.
ABSTRACT | FULL TEXT  

Measuring Percutaneous Coronary Intervention Quality by Simple Case Volume
Kuntz and Normand
Circulation 2005;112:1088-1091.
FULL TEXT  

Optimal Locoregional Treatment in Gastric Cancer
Jansen et al.
JCO 2005;23:4509-4517.
ABSTRACT | FULL TEXT  

Outcome Results of the 1996-1999 Patterns of Care Survey of the National Practice for Patients Receiving Radiation Therapy for Carcinoma of the Esophagus
Suntharalingam et al.
JCO 2005;23:2325-2331.
ABSTRACT | FULL TEXT  

Surgical Prevention of Cancer
Bertagnolli
JCO 2005;23:324-332.
ABSTRACT | FULL TEXT  

Surgery for primary supratentorial brain tumors in the United States, 1988 to 2000: The effect of provider caseload and centralization of care
Barker et al.
Neuro Oncol Duke 2005;7:49-63.
ABSTRACT  

National Trends in Outcomes for Esophageal Resection
Dimick et al.
Ann. Thorac. Surg. 2005;79:212-216.
ABSTRACT | FULL TEXT  

Does it matter what a hospital is "high volume" for? Specificity of hospital volume-outcome associations for surgical procedures: analysis of administrative data
Urbach and Baxter
Qual Saf Health Care 2004;13:379-383.
ABSTRACT | FULL TEXT  

Does the Who and How of Surgery in Bladder Cancer Matter?
Lange and Lin
JCO 2004;22:2762-2764.
FULL TEXT  

Quality of cancer care
Vardy and Tannock
Ann Oncol 2004;15:1001-1006.
ABSTRACT | FULL TEXT  

Does Pediatric Surgical Specialty Training Affect Outcome After Ramstedt Pyloromyotomy? A Population-Based Study
Langer and To
Pediatrics 2004;113:1342-1347.
ABSTRACT | FULL TEXT  

Does it matter what a hospital is "high volume" for? Specificity of hospital volume-outcome associations for surgical procedures: analysis of administrative data
Urbach and Baxter
BMJ 2004;328:737-740.
ABSTRACT | FULL TEXT  

Hospital Teaching Status and Outcomes of Complex Surgical Procedures in the United States
Dimick et al.
Arch Surg 2004;139:137-141.
ABSTRACT | FULL TEXT  

Impact of Hospital Procedure Volume on Surgical Operation and Long-Term Outcomes in High-Risk Curatively Resected Rectal Cancer: Findings From the Intergroup 0114 Study
Meyerhardt et al.
JCO 2004;22:166-174.
ABSTRACT | FULL TEXT  

National Variation in Operative Mortality Rates for Esophageal Resection and the Need for Quality Improvement
Dimick et al.
Arch Surg 2003;138:1305-1309.
ABSTRACT | FULL TEXT  

Surgeon Volume and Operative Mortality in the United States
Birkmeyer et al.
NEJM 2003;349:2117-2127.
ABSTRACT | FULL TEXT  

Regionalization of High-Risk Surgery and Implications for Patient Travel Times
Birkmeyer et al.
JAMA 2003;290:2703-2708.
ABSTRACT | FULL TEXT  

Mortality and morbidity in gastro-oesophageal cancer surgery: initial results of ASCOT multicentre prospective cohort study
McCulloch et al.
BMJ 2003;327:1192-1197.
ABSTRACT | FULL TEXT  

Differences in Treatment and Outcome Between African-American and White Women With Endometrial Cancer
Randall and Armstrong
JCO 2003;21:4200-4206.
ABSTRACT | FULL TEXT  

One Thousand Fifty-Six Hepatectomies Without Mortality in 8 Years
Imamura et al.
Arch Surg 2003;138:1198-1206.
ABSTRACT | FULL TEXT  

Association of Hospital Procedure Volume and Outcomes in Patients with Colon Cancer at High Risk for Recurrence
Meyerhardt et al.
ANN INTERN MED 2003;139:649-657.
ABSTRACT | FULL TEXT  

The Effect of Clustering of Outcomes on the Association of Procedure Volume and Surgical Outcomes
Panageas et al.
ANN INTERN MED 2003;139:658-665.
ABSTRACT | FULL TEXT  

Transsphenoidal Surgery for Pituitary Tumors in the United States, 1996-2000: Mortality, Morbidity, and the Effects of Hospital and Surgeon Volume
Barker et al.
J. Clin. Endocrinol. Metab. 2003;88:4709-4719.
ABSTRACT | FULL TEXT  

Treatment of Locally Advanced Pancreatic Cancer in the Real World: Population-Based Practices and Effectiveness
Krzyzanowska et al.
JCO 2003;21:3409-3414.
ABSTRACT | FULL TEXT  

In-Hospital Morbidity and Mortality after Endovascular Treatment of Unruptured Intracranial Aneurysms in the United States, 1996-2000: Effect of Hospital and Physician Volume
Hoh et al.
Am. J. Neuroradiol. 2003;24:1409-1420.
ABSTRACT | FULL TEXT  

Mortality during hospitalisation for pneumonia in Alberta, Canada, is associated with physician volume
Marrie et al.
Eur Respir J 2003;22:148-155.
ABSTRACT | FULL TEXT  

Hospital Volume and Operative Mortality in Cancer Surgery: A National Study
Finlayson et al.
Arch Surg 2003;138:721-725.
ABSTRACT | FULL TEXT  

Differences in operative mortality between high- and low-volume hospitals in Ontario for 5 major surgical procedures: estimating the number of lives potentially saved through regionalization
Urbach et al.
CMAJ 2003;168:1409-1414.
ABSTRACT | FULL TEXT  

Relation of Hospital Volume to Colostomy Rates and Survival for Patients With Rectal Cancer
Hodgson et al.
JNCI J Natl Cancer Inst 2003;95:708-716.
ABSTRACT | FULL TEXT  

Adjuvant therapy in pancreatic cancer: historical and current perspectives
Neoptolemos et al.
Ann Oncol 2003;14:675-692.
ABSTRACT | FULL TEXT  

The volume-outcome relationship: from Luft to Leapfrog
Shahian and Normand
Ann. Thorac. Surg. 2003;75:1048-1058.
ABSTRACT | FULL TEXT  

Hospital experience and outcomes for esophageal variceal bleeding
MORSS DY et al.
Int J Qual Health Care 2003;15:139-146.
ABSTRACT | FULL TEXT  

Perspectives on the Value of American Society of Clinical Oncology Clinical Guidelines as Reported by Oncologists and Health Maintenance Organizations
Bennett et al.
JCO 2003;21:937-941.
ABSTRACT | FULL TEXT  

Colonic Interposition After Esophagectomy for Cancer
Davis et al.
Arch Surg 2003;138:303-308.
ABSTRACT | FULL TEXT  

Association of Volume and Volume-Independent Factors With Accuracy in Screening Mammogram Interpretation
Beam et al.
JNCI J Natl Cancer Inst 2003;95:282-290.
ABSTRACT | FULL TEXT  

Surgical volume and quality of care for esophageal resection: do high-volume hospitals have fewer complications?
Dimick et al.
Ann. Thorac. Surg. 2003;75:337-341.
ABSTRACT | FULL TEXT  

Role of Surgeon Volume in Radical Prostatectomy Outcomes
Hu et al.
JCO 2003;21:401-405.
ABSTRACT | FULL TEXT  

Hepatic Resection in the United States: Indications, Outcomes, and Hospital Procedural Volumes From a Nationally Representative Database
Dimick et al.
Arch Surg 2003;138:185-191.
ABSTRACT | FULL TEXT  

Postoperative Complication Rates After Hepatic Resection in Maryland Hospitals
Dimick et al.
Arch Surg 2003;138:41-46.
ABSTRACT | FULL TEXT  

"The Guard Dies, It Does Not Surrender!" Progress in the Management of Small-Cell Lung Cancer?
Johnson
JCO 2002;20:4618-4620.
FULL TEXT  

Implementation of a Voluntary Hospitalist Service at a Community Teaching Hospital: Improved Clinical Efficiency and Patient Outcomes
Auerbach et al.
ANN INTERN MED 2002;137:859-865.
ABSTRACT | FULL TEXT  

Effects of Physician Experience on Costs and Outcomes on an Academic General Medicine Service: Results of a Trial of Hospitalists
Meltzer et al.
ANN INTERN MED 2002;137:866-874.
ABSTRACT | FULL TEXT  

Is Volume Related to Outcome in Health Care? A Systematic Review and Methodologic Critique of the Literature
Halm et al.
ANN INTERN MED 2002;137:511-520.
ABSTRACT | FULL TEXT  

Will Volume-Based Referral Strategies Reduce Costs Or Just Save Lives?
Birkmeyer et al.
Health Aff (Millwood) 2002;21:234-241.
ABSTRACT | FULL TEXT  

Are Deaths Within 1 Month of Cancer-Directed Surgery Attributed to Cancer?
Welch and Black
JNCI J Natl Cancer Inst 2002;94:1066-1070.
ABSTRACT | FULL TEXT  

Does delivery volume of family physicians predict maternal and newborn outcome?
Klein et al.
CMAJ 2002;166:1257-1263.
ABSTRACT | FULL TEXT  

Hospital Volume and Surgical Mortality in the United States
Birkmeyer et al.
NEJM 2002;346:1128-1137.
ABSTRACT | FULL TEXT  

Variations in Morbidity after Radical Prostatectomy
Begg et al.
NEJM 2002;346:1138-1144.
ABSTRACT | FULL TEXT