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Interpreting the Volume-Outcome Relationship in the Context of Cancer Care (2001)

Chapter: Appendix A Volume and Outcome in Cancer Surgery

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Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
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Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
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Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
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Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 16
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 17
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 18
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 19
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 20
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 21
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 22
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 23
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 24
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 25
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 26
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 27
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 28
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 29
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 30
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
×
Page 31
Suggested Citation:"Appendix A Volume and Outcome in Cancer Surgery." Institute of Medicine and National Research Council. 2001. Interpreting the Volume-Outcome Relationship in the Context of Cancer Care. Washington, DC: The National Academies Press. doi: 10.17226/10160.
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Appendix A Volume and Outcome in Cancer Surgery Excerpted from “How Is Volume Related to Quality in Health Care? A Systematic Review of the Research Literature,” by Ethan A. Halm, MD, MPH, Clara Lee, MD, MPP, and Mark R. Chassin, MD, MPP, MPH, Department of Health Policy, Mount Sinai School of Medicine Prepared for: Institute of Medicine, National Academy of Sciences Division of Health Care Services, Committee on Quality of Care in America National Cancer Policy Board Workshop Interpreting the Volume–Outcome Relationship in the Context of Health Care Quality May 1, 2000 VOLUME AND OUTCOME IN CANCER SURGERY We examined a total of 38 studies on cancer (criteria for rating the quality of published studies and literature review methods are described on pages 22–25). All of the eight studies of medical treatment of cancer were excluded because none of them looked at volume as an independent variable. Of the 30 studies of surgical treatment, 10 were excluded. The most common reason for exclusion was a sample that was not community- or population-based (7 studies). Two studies did not evaluate volume as an independent variable (Gordon, 1998; Whit- tle, 1998). One paper was a review article, not primary research (Steele, 1996). Thus, 20 papers, all about cancer surgery, were included in the systematic review. Three of these studies looked at more than one procedure (Hannan, 2000; Gordon, 1999; Begg, 1998). To analyze these articles, we examined the data for each procedure separately. In total, 11 papers studied pancreatic resec- tion, five studied colorectal resection, three studied esophagectomy, three stud- ied lung resection, and two studied breast surgery (see attached summaries). The three articles that looked at other cancer procedures are summarized separately in a table called “Cancer Miscellaneous.” We did not include other papers that studied these operations for benign as well as malignant disease, with the exception of Gordon (1999). We included 13

14 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP Gordon (1999) because it studied pancreaticoduodenectomy and esophagec- tomy, both of which are rarely performed for benign disease. Pancreatic Resection Eleven studies evaluated pancreatic resection. The quality scores varied greatly, ranging from 3 to 10, with a median of 7. The study with the lowest qual- ity score had a small sample that was not representative of the entire population and did not perform any risk adjustment (Wade, 1996). The study with the highest quality score had a large, representative sample, and it examined physician vol- ume, hospital volume, and the interaction between the two (Lieberman, 1995). The unit of analysis was the hospital for all studies, except for two that looked at both surgeon and hospital volume (Lieberman, 1995; Sosa, 1998). No study evaluated appropriateness of patient selection. The definition of low hos- pital volume ranged from less than 1 to less than 9 procedures per year. Begg et al. defined volume as the annual volume of procedures done on Medicare pa- tients. Two studies of Maryland had only one high-volume hospital (Gordon, 1995; Gordon, 1999). In Lieberman and colleagues’ study of New York State, two hospitals were high-volume, and four surgeons were high-volume. The two analyses of surgeon and hospital volume interaction were limited by the fact that most of the high-volume surgeons practiced only in high-volume hospitals. No study effectively addressed the question of “volume of what.” Gordon et al. studied the association between the total volume of 6 “complex gastrointesti- nal” procedures (total colectomy, esophagectomy, total gastrectomy, hepatic lobectomy, biliary tract anastomosis, and pancreaticoduodenectomy) and indi- vidual procedure mortality. They did not also study, however, the association between individual procedure volumes and mortality (Gordon, 1999). No study evaluated the appropriateness of patient selection. Risk adjustment was based almost exclusively on administrative data. Only Begg et al. used some clinical data (cancer staging from the Survival, Epide- miology, and End Results database). None of the studies examined clinical pro- cesses. Inpatient death was the primary outcome of interest. Three studies looked at death beyond the inpatient stay (Simunovic, 1999; Birkmeyer, 1999a; Birkmeyer, 1999b), and one measured rates of complications, specifically infec- tion and hemorrhage (Glasgow, 1996). Other complications such as pancreatic or biliary leak, gastric dysmotility, pneumonia, and other outcomes such as re- currence and quality of life were not examined. Of the nine studies that looked at hospital volume only, all but one (Wade, 1996) found a significant relationship between volume and outcomes. The high- est quality score of 8 was achieved by a study of 1705 pancreatectomies at 298 hospitals in California from 1990 to 1994 (Glasgow, 1996). In this study, the risk-adjusted mortality at high-volume hospitals (> 50 cases per year) was 3.5%, compared to 14% at low-volume hospitals (< 5 cases per year).

APPENDIX A 15 Lieberman et al. (1995) analyzed both physician and hospital volumes; 1,972 procedures were performed by 748 surgeons in 184 hospitals in New York State from 1984 to 1991. In separate analyses of surgeon volume and hospital volume, high-volume surgeons (> 41 cases per year) had lower risk-adjusted mortality rates than low-volume surgeons (< 9 cases per year)—6% versus 13%, and high-volume hospitals (> 8 cases per year) had lower risk-adjusted mortality rates than low-volume hospitals (< 10 cases per year)—5% versus 19%. When surgeon volume and hospital volume were analyzed together, however, only hospital volume was significant. Sosa et al. (1998) analyzed both physician and hospital volumes for 1,236 procedures by 373 surgeons at 48 hospitals in Maryland. They found that the relative risk of death at low-volume hospitals (< 5 cases per year) was 19 times that at high-volume hospitals (> 20 cases per year). Analyzing physician and hospital volume together, they found hospital volume to be significant regard- less of physician volume. Although the studies on pancreatic resection had a great deal of methodo- logical heterogeneity, they suggested that outcomes were related to provider volume and to hospital volume in particular. The magnitude of this volume ef- fect was relatively large compared to most of the other procedures we studied. This is a function of both the high absolute mortality rate for pancreatic cancer as well as a very strong volume and outcome relationship. The number needed to be treated by a high-volume provider to prevent one inpatient death attribut- able to low volume was only 10 to 15 for most higher-quality studies. Esophagectomy The three studies of esophagectomy had low quality scores (6, 6, and 8). The two lower-scoring studies had relatively small sample sizes—518 patients in one (Gordon, 1999) and 503 patients in another (Begg, 1998). The unit of analysis was the hospital in all three studies. The definition of low volume was relatively similar across studies, ranging from less than 6 to less than 10 proce- dures per year. Begg et al. measured volume of Medicare cases only. All studies performed some risk adjustment, and only one utilized clinical data (Begg, 1998). No study evaluated clinical processes such as operative approach (ab- dominal versus thoracoabdominal) and method of reconstruction. The only outcome evaluated was inpatient mortality. No study examined long-term survival, recurrence, or quality of life. Complications such as anasto- motic leak, respiratory failure, pneumonia, and digestive dysfunction were not measured. All three studies found large differences in mortality between low-volume and high-volume hospitals. Gordon and colleagues found that the relative risk of death at a low-volume hospital was 3.8 times that at a very-high-volume hospital, although there was only one institution in this latter category (Gordon, 1999).

16 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP Begg et al. found that the risk-adjusted mortality at high-volume hospitals was 3.4%, compared to 17.3% at low-volume hospitals. Patti et al. (1998) found similar mortality rates—6% at high-volume hospitals and 17% at low-volume hospitals. This study had the highest quality score of 8, in part because of its large size. Overall, the magnitude of the volume and outcome relationship for esopha- gectomy was striking. The number needed to treat by a high-volume provider to prevent one inpatient death attributable to low volume was seven to nine patients. Breast Cancer Surgery The two studies of breast cancer surgery had relatively high quality scores (10 and 11) because they had large numbers of patients, surgeons, hospitals, and adverse events, and because they utilized clinical data from cancer registries in their risk adjustment models. The unit of analysis was the hospital in one study (Roohan, 1998) and the surgeon in the other (Sainsbury, 1995). Neither study looked at the appropriateness of patient selection. Roohan et al. defined “very low” hospital volume as fewer than 10 cases per year. Sainsbury et al. defined low surgeon volume as fewer than 30 cases per year. Sainsbury et al. attempted to include extent of disease and tumor grade in their risk-adjustment model, though this information was missing for 50% of patients. The two studies were noteworthy for their measurement of clinical proc- esses. Roohan et al. included the type of operation (mastectomy or breast- conserving surgery) as an independent variable in the multivariate analysis. Sainsbury et al. included the percentage of patients treated by mastectomy (ver- sus local excision), chemotherapy, hormone therapy, radiation therapy, or sur- gery alone for each surgeon. These two studies were unique in that they both selected a long-term outcome (5-year survival) as their dependent variable. Neither study measured other outcomes such as recurrence, complications of surgery, or complications of adjuvant therapy. Roohan et al. looked at 47,890 cases of breast cancer surgery performed in 266 hospitals in New York State from 1984 to 1989. In a multivariate regression model, they found volume to be related to 5-year mortality, with a clear “dose- response” relationship. The increased risk of death was 19% in moderate- volume versus high-volume hospitals, 30% in low-volume versus high-volume hospitals, and 60% in very-low-volume versus high-volume hospitals. The authors conjectured that since breast surgery has negligible operative and inpa- tient mortality, the volume–outcome relationship might be caused by higher- volume hospitals providing more effective adjuvant treatment. Sainsbury et al. studied 12,861 cases of breast cancer surgery performed by 180 surgeons in the Yorkshire Regional Health Authority area from 1979 to 1988. Risk adjustment included age, extent of disease, tumor grade, socioeco- nomic status, date of treatment, and type of therapy (surgery, radiation, chemo- therapy, hormone therapy, surgery alone). They found that the risk of death was

APPENDIX A 17 significantly lower for patients of high-volume surgeons (greater than 29 cases per year) compared to low-volume surgeons (fewer than 10 cases per year). There was no difference in survival between moderate-volume (10 to 29 cases per year) and low-volume surgeons. The volume effect was slightly smaller after risk ad- justment (risk ratio of 0.86 versus 0.82 before adjustment). Variation among sur- geons in use of mastectomy, radiation, chemotherapy, hormone therapy, and sur- gery alone accounted for 8% of the variation in survival. Surgeon volume and use of chemotherapy accounted for 20 to 25% of the variation in survival. Lung Resection The quality scores of the three studies of lung resection were relatively high (8, 8, and 10). The numbers of patients, physicians, hospitals, and adverse events were all high. The unit of analysis was the hospital in two studies (Begg, 1998; Romano, 1992) and both hospital and physician in one study (Hannan, 2000). No study evaluated the appropriateness of patient selection. The three studies looked at different types of lung resection—lobectomies (Hannan, 2000), pneu- monectomies (Begg, 1998), and all resections (Romano, 1992). The definitions of low hospital volume were heterogeneous, ranging from less than 6 to less than 38 procedures per year. Risk adjustment was based on administrative data in two of the studies (Hannan, 2000; Romano, 1992) and clinical data in one (Begg, 1998). No study looked at clinical processes of care. The outcome of interest was inpatient death in all three studies. Complications such as bronchopleural fistula, respiratory failure, and pneumonia were not measured. In addition, no study evaluated other outcomes such as long-term survival, recurrence, or quality of life. In the study with the highest quality score of 10, Hannan et al. (2000) looked at 6,954 lobectomies by 373 surgeons at 178 hospitals. The risk-adjusted mortality rate at low-volume hospitals (>37 cases per year) was 1.65% higher than at high-volume hospitals (>169 cases per year). There was no difference between medium-volume and high-volume hospitals. The vast majority of hos- pitals were low-volume (133 hospitals). Only 4 hospitals were high-volume. No significant relationship between surgeon volume and outcome was found Begg and colleagues examined 1,375 pneumonectomies performed on Medicare patients at 313 hospitals in the United States. They utilized clinical data for risk adjustment. No difference in outcomes existed between high- volume and low-volume hospitals. Romano and colleagues found 40% lower risk of death after pneumonectomy at high-volume hospitals compared to low- volume hospitals. They also found a similar volume–outcome relationship for lesser resections.

18 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP Colorectal Resection The five studies of colorectal cancer resection had quality scores ranging from 7 to 10, with a median of 9. The studies were very heterogeneous. Three studies evaluated resections of all types of colorectal cancer (Hannan, 2000; Harmon, 1999; Parry, 1999), one looked at total colectomy for benign and ma- lignant disease (Gordon, 1999), and one looked at resections for rectal cancer (Porter, 1998). The unit of analysis was the hospital in one study (Gordon, 1999), the physician in one study (Porter, 1998), and both hospitals and physi- cians in three (Hannan, 2000; Harmon, 1999; Parry, 1999). The definition of low volume was variable, even among the three studies that looked at volume of all colorectal resections. Among these three studies, the definition of low surgeon volume ranged from less than 6 to less than 12 proce- dures per year. The definition of low hospital volume ranged from less than 40 to less than 84 per year. Gordon et al. looked at the relationship between 6 com- plex gastrointestinal procedures including total colectomy and the outcomes of total colectomy. All studies performed risk adjustment, and two studies (Porter, 1998; Parry, 1999) used clinical data. Two studies examined clinical processes, but neither incorporated the processes into their risk adjustment model. Parry et al. meas- ured whether or not an abdominoperineal resection was performed, use of ultra- sound or CT scan, and operating “after hours.” Porter et al. looked at the type of operation (low anterior resection versus abdominoperineal resection) and the use of adjuvant therapy. The outcome studied was primarily inpatient mortality. One study (Parry, 1999) measured local recurrence rates as well as disease-specific survival. No study measured complications such as anastomotic leak, intra- abdominal abscess, wound infection, or genitourinary dysfunction. Three of the four studies that assessed hospital volume did not find a sig- nificant relationship to outcomes. Harmon et al. studied all resections in Mary- land and found a trend toward lower mortality at high-volume hospitals, but this was not significant (odds ratio 0.78, p < 0.10). Parry et al. studied all resections in the northwestern United Kingdom and found no relationship between volume and outcomes. Gordon et al. found no relationship between volume of complex gastrointestinal surgery and outcome of total colectomy. The only study to find a significant relationship for hospital volume found that the risk-adjusted mortal- ity rate at low-volume hospitals was 1.9% higher than at high-volume hospitals (Hannan, 2000). Of the four studies that measured physician volume, three found a signifi- cant volume–outcome relationship. Only Parry et al. found no relationship be- tween physician volume and outcomes. Porter et al. found that patients of low- volume surgeons had worse disease-specific survival than patients of high- volume surgeons (hazard ratio = 1.40) and a higher risk of local recurrence (haz- ard ratio = 1.80). High-volume surgeons were more likely to perform a low ante-

APPENDIX A 19 rior resection as might be expected. They were no more likely, however, to use adjuvant therapy than low-volume surgeons were. Three studies analyzed physician volume and hospital volume together. The physician effect found by Hannan et al. disappeared when hospital volume was controlled for in the analysis. Harmon et al. found that surgeon volume was re- lated to volume regardless of hospital volume. The studies of volume and outcome in colorectal surgery do not uniformly find a significant relationship. The magnitude of the volume effect on mortality is relatively modest—an absolute difference in inpatient mortality of 1% to 2% cor- responding to a number needed to treat of 50–100. SUMMARY The 20 studies of cancer surgery suggest that a significant relationship be- tween volume and outcomes does exist. The largest differences between low- and high-volume providers were found for the most complicated operations in rare cancers—pancreatectomy and esophagectomy. For colorectal resection and lung resection, two operations for more common cancers, the relationship be- tween volume and outcome is not as clear. The common methodological issues for these studies point to a need for more clinical data. Information about the type of tumor and cancer stage would be highly desirable, particularly in studies that look at long-term survival. An exami- nation of the different clinical processes being employed and how they vary with provider volume might elucidate the differences in outcomes. For example, the use of adjuvant therapies is particularly important but has not been well-studied with respect to volume. The roles of other providers besides the surgeon have also not been examined. Particularly when long-term survival is being evaluated, charac- teristics of other providers who care for the patient years after surgery, such as the medical oncologist and radiation oncologist, would be relevant. More appropriate referral to these providers or better coordination of the many elements of cancer care, such as diagnostic testing, adjuvant therapy, and follow-up surveillance, may underlie the hospital volume effects that have been found. It is worth noting that the literature on volume and outcomes in cancer has disproportionately focused on rare operations for rare cancers. For the most common cancer operations—breast cancer surgery, colon resection, and lung resection—we found 10 studies that met our inclusion criteria. By contrast, the most rare operations—esophagectomy and pancreatectomy—had 13 publica- tions. In addition, we found no studies of medical treatment of cancers.

20 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP CRITERIA FOR RATING THE QUALITY OF PUBLISHED STUDIES We developed a scoring system to assess the quality of the research studies included in our systematic review. The full list of criteria is described on page 23. Our aim was to create a quantitative method of assessing the research design of the studies we reviewed such that higher scores would reflect increasing like- lihood of the study’s ability to discern generalizable conclusions about the na- ture and magnitude of the relationship between volume and outcome. The first four criteria assess various aspects of the patient sample used in the research. We assigned one point if the sample was representative of the general popula- tion of all patients who might receive the treatments under study. Thus, studies of managed care plan enrollees or Medicare beneficiaries were not considered representative. We assigned two points if the study included patients of 50 or more physicians and 20 or more hospitals. If only one of these criteria was met, we assigned one point. No points were assigned if neither criterion was met. In some studies authors reported the number of hospitals in their sample but not the number of treating physicians. In these cases we estimated the number of physi- cians by assuming it would be at least equal to the number of hospitals. The vast majority of these studies included hundreds of hospitals from administrative databases, so we estimated the number of physicians as > 50 for scoring this criterion. If the total sample size was 1,000 patients or more, we assigned one point. Because statistical power to detect significant relationships in logistic regression models depends more on the total number of adverse events repre- sented in the sample than on total sample size (and because the various condi- tions and procedures in this literature have widely varying adverse event rates), we assigned 2 points if the total number of adverse events was greater than 100, one point if it was 21–100, and no points if it was 20 or less. We assigned no points if the study assessed the relationship between out- come and either hospital or physician volume. If both were assessed separately, we assigned one point. If the joint relationships of hospital and physician vol- ume were assessed independently in a multivariate analysis, we assigned 2 points. And if a study examined both of these and the volume of another impor- tant component of the care process, we assigned 3 points. If the appropriateness of patient selection was not addressed, we assigned no points. If appropriateness was measured, we assigned 1 point. If it was measured and taken into account in the analysis of the volume–outcome relationship, we assigned 2 points. If volume was analyzed in only 2 categories, we assigned no points. If more than 2 categories were assessed or if volume was treated as a continuous vari- able, we assigned 1 point to credit a more sophisticated assessment of a possible dose-response relationship. In considering the various ways in which outcomes might be risk-adjusted, we assigned no points if no risk-adjustment at all was done. If data from insurance claims, hospital discharge abstract databases, or

APPENDIX A 21 other sources of administrative data were used, we assigned 1 point. If data from clinical sources (e.g., medical records or prospectively designed clinical regis- tries) were used for risk-adjustment, we assigned 2 points. If clinical data were used in a logistic regression model that demonstrated good calibration by the Hosmer-Lemeshow test and good discrimination (by a C-statistic of 0.75 or greater), we assigned 3 points. If specific clinical processes of care were not measured, we assigned no points. If a single process was measured and its impact on risk-adjusted out- comes assessed, we assigned 1 point. If 2 or more such processes were measured and evaluated, we assigned 2 points. Finally, if death was the only outcome evaluated, we assigned no points. If other adverse outcomes in addition to mor- tality were assessed, we assigned 2 points. Quality scores were summed across all 10 criteria for each study. The maximum possible total score was 18. Literature Review Methods We performed two electronic subject-based searches of the literature on MEDLINE (1966–1999). A professional reference librarian assisted us in the development of our search strategy We developed a list of search terms based on subject headings from articles known to be highly relevant to our topic and from the official indexing terms of the MEDLINE database. We performed multiple searches with combinations of these terms and evaluated the results of those searches for sensitivity and speci- ficity, with respect to our topic of volume and outcomes. The search algorithm that yielded the greatest number of highly relevant articles combined the condi- tions with the terms volume, utilization, frequency, statistics, and outcomes. In order to broaden our search to include articles on regionalization of care, we added another search that combined the conditions with the term regionalization. We also performed MEDLINE searches on authors known to have pub- lished widely on the study topic, and we searched the Cochrane Collaboration Database for systematic reviews. In addition to performing electronic database searches, we consulted experts in the field for further references. Finally, we reviewed the references cited by each article that was ultimately included. We did not hand-search any journals. This review was limited to the English- language research literature. This paper includes the findings of our review of cancer-related procedures and conditions. Study inclusion criteria were: 1. Time: patient cohorts treated from 1980 forward. 2. Sample: community- or population-based sample—case series or con- venience samples were excluded. 3. Multiple publications from the same database excluded; only the most recent or most complete publication was included.

22 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP 4. Health outcome(s) must be assessed as the dependent variable(s). 5. Volume must be an independent variable. We limited the review to studies of patients treated from 1980 to the pres- ent, because of the rapidity of changes in hospital care, available treatments, and surgical techniques. In our view, data from patient cohorts prior to 1980 would have questionable relevance to today’s policy issues. In a few instances, we in- cluded studies if part of their patient sample included patients treated in 1978 or 1979, but most of the sample comprised patients from the 1980s. We excluded studies from single institutions, from voluntary registries, or other convenience samples because of the weak generalizability of such studies. We excluded a few studies in which the only dependent variable was a composite of deaths or long lengths of stay, because, formulated in this way, the dependent variable was not purely a health outcome. We also excluded a few studies in which the only dependent variable was a composite of death or complications, with the latter determined solely by secondary diagnosis codes in administrative data- bases. These studies were excluded because of the notorious unreliability of using such data to identify complications. In general, we excluded multiple pub- lications from the same set of data, selecting only the most recent or complete, unless different publications reported substantially different analyses (e.g., one reported the relationship of hospital volume to outcome and another analyzed physician volume and outcome). Three reviewers assessed the articles for inclusion or exclusion, with at least two reviewers independently examining each article and applying the criteria. Discrepancies in the application of the criteria were resolved by discussion be- tween the reviewers. Our final criteria for quality assessment and the scoring system were described earlier and are listed in on page 23. The same pair of re- viewers who assessed each article for inclusion or exclusion then independently evaluated each article and assigned quality scores. Discrepancies were resolved by discussion between the two reviewers.

RATING THE QUALITY OF RESEARCH ON VOLUME AND OUTCOME Objective of Scoring System: designed to measure the degree to which the study design is likely to reveal generalizable conclusions about the magnitude and nature of the relationship between volume and outcome. Characteristic Values Scores 1. Representativeness of sample Not Representative 0 1 2. Number of hospitals or doctors H < 20 and/or MD < 50 H > 20 and MD >50 0 1 2 3. Total sample size (cases) < 1000 > 1000 0 1 4. Number of adverse events < 20 21–100 > 100 0 1 2 5. Unit of analysis Hospital or MD Both separately Both together Both + 0 1 2 3 6. Appropriateness of patient se- not measured measured separately measured and analyzed 0 1 2 lection separately 7. Volume 2 categories Multiple 0 1 8. Risk adjustment none admin only clinical data clinical + C >.75 0 1 2 3 and H/L test + 9. Clinical processes of care not measured One 2+ 0 1 2 10. Outcomes death only death + 0 1 TOTAL POSSIBLE POINTS = 18 23 23

24 PANCREAS 24 Study Population Time Patient MD Hospital Unit Primary Risk Definition Volume: Score period # # # of outcome adjust- of Outcomes analysis ment low results data volume source Gordon All 1989– 1092 NS 51 Hosp Inpt death Admin Hosp: Vol RR 7 1999 Maryland 1997 < 10/yr < 10 12.5 Benign & 11–20 10.4 malignant 21–50 6.3 > 200 1 Birkmeyer Medicare 1992– 7229 NS Hosp 3yr death Admin Hosp OR = 0.69 7 1999a US 1995 1772 Very Benign & low: < 1 malignant Low: 1–2 High: > 5 Birkmeyer Medicare 1992– 7229 NS Hosp Inpt death Admin Hosp Inpt death: 7 1999b US 1995 1772 30d death Very 16% vs. 4.1% Benign & low: < 1 (very high 1.7%) malignant Low: 1–2 30d death: High: > 5 12.9 vs. 3.0% Sosa All 1990– 1236 373 48 MD Inpt death Admin MD: LVH vs. HVH: 9 1998a Maryland 1995 Hosp Low: < 5, RR = 19.3 Both High: > 50 HVH better, Hosp: regardless of MD Low: < 5 volume High: > 20 (continued)

Begg Medicare 1984– 742 NS 252 Hosp Inpt death Clinical Low: < 6 Mortality: 6 1998 US 1993 high: 12.9 vs. 5.8% > 10/yr Simunovic All 1988/89 842 NS 68 Hosp Inpt death Admin < 22 LVH: OR = 5.1 6 1999 Ontario or 64d death MVH: OR = 4.5 1994/95 Glasgow All 1990– 1705 NS 298 Hosp Inpt death Admin Low: 1–5 RAMR: 8 1996 CA 1994 Bleeding High: > 50 14 vs. 3.5% Infection Imperato Medicare 1991– 579 NS 117 Hosp Inpt death Admin Low: Mortality: 5 1996 NY 1994 1–5/yr 14.3 vs. 2.2% high: (RR 6.87) > 25/yr Wade Dept of 1989– 130 NS 111 Hosp Inpt death None <1 Mortality 3 1996 Defense 1994 < 1: 6% US 1–2: 9% > 2: 9% (no p value given) Lieberman All 1984– 1972 748 184 MD Inpt death Admin MD: < 9 MD: 10 1995 NY 1991 Hosp Hosp: < 10 6 vs. 13%; Both Hosp: 5 vs. 18.9%; Both: Only hos- pital volume is important Gordon All 1988– 501 NS 39 Hosp Inpt death Admin Low: Mortality: 6 1995 Maryland 1993 < 1–5/yr 19vs. 2.2% (RR high: = 8.7) > 20/yr OR: odds ratio RR: relative risk NS: not specified LVH: low-volume hospital 25 25

26 ESOPHAGUS 26 Study Population Time Patient MD Hospital Unit of Primary Risk Definition Volume: Score period # # # analysis outcome adjustment of low Outcomes data source volume results Gordon All 1989– 518 NS 51 Hosp Inpt Admin Hosp: Vol RR 6 1999 Maryland 1997 death < 10/yr < 10 3.8 (Benign and Volume of 6 11–20 4.0 malignant) complex GI 21–50 2.4 procedures > 200 1.0 Begg Medicare 1984– 503 NS 190 Hosp Inpt Clinical Hosp: Mortality 6 1998 US 1993 death Low: < 5/yr 17.3 vs. high: > 11/yr 3.4% Patti All CA 1990– 1561 NS 273 Hosp Inpt Admin Hosp: Mortality 8 1998 1994 death Low: < 5/yr 17 vs. 6% High: > 30/yr RR: Relative Risk

BREAST Study Population Time Patient MD Hospital Unit of Primary Risk Definition Volume: Score period # # # analysis outcome adjustment of low Outcomes data source volume results Roohan All women 1984− 47890 NS 266 Hosp 5 yr Clinical Hosp: OR = 1.6 10 1998 NY 1989 survival Low: <10/yr high: >149/yr Sainsbury All women 1979− 12861 180 NS MD 5 yr Clinical MD: Adjusted 11 1995 Yorkshire, 1988 survival <30/yr Vol RR Ratio UK <10 1.0 10−29 0.97 30−49 0.85 > = 50 0.86 Abbreviations: OR: odds ratio RR: relative risk NS: not specified 27 27

28 LUNG 28 Study Population Time Patient MD Hospital Unit of Primary Risk Definition Volume: Score period # # # analysis outcome adjustment of low Outcomes Data source volume Results Hannan All 1994– 6954 373 178 MD Inpt death Admin MD: Hosp: RAMR 10 in press NY 1997 Hosp < 23/yr for LVH Lobectomies Both Hosp: 1.65% > HVH < 38/yr MD: no relationship Begg Medicare 1984– 1375 NS 313 Hosp 30 day Clinical Hosp: No 8 1998 US 1993 mortality < 6/yr relationship Pneumo- nectomies Romano All 1983– 12439 NS 389 Hosp Inpt death Admin Hosp: Lesser 8 1992 CA 1986 < 9/yr resections All (high- rela- resections tive to low- volume): OR = 0.6 Pneumonec- tomy: OR = 0.6 Abbreviations: LVP: low-volume physician LVH: low-volume hospital HVP: high-volume physician HVH: high-volume hospital RAMR: risk-adjusted mortality rate OR: odds ratio

COLORECTAL Study Population Time Patient MD # Hospital Unit of Primary Risk Definition of Volume: Outcomes Score period # # analysis outcome adjustment low volume results data source Hannan All 1994– 22128 2052 229 MD Inpt death Admin MD: low: < 12 RAMR for LVH 10 in press NY 1997 Hosp high: > 34 1.93% > HVH; No Both Hosp: MD effect when hosp low: < 84 volume controlled high: > 253 Harmon All 1992– 9739 812 50 MD Inpt death Admin MD: < 6/yr MD: HVS vs. LVS; 10 1999 Maryland 1996 Hosp Hosp: < 40/yr OR = .64; Hosp: HVH Both vs. LVH; OR = .78; MVS at HVH/MVP equiv to HVS; HVS better at any hosp Parry All 1993 927 123 39 MD 30 day Clinical MD: < 7 in 6 No relationship 9 1999 NW UK (6 Hosp death; 3 year mos mos) survival Hosp: < 30 in 6 mos Gordon All 1989– 1015 NS 51 Hosp Inpt death Admin Hosp: < 10/yr No relationship 8 1999 Maryland 1997 Total colectomy Porter All 1983– 683 52 5 MD Local Clinical MD: < 21/yr Local recurrence HR = 7 1998 Edmonton 1990 recurrence 1.8; DSS: HR = 1.4 Rectal Disease- HVP no more likely to cancer specific give adjuvant Rx; survival HVP more likely to do LAR RAMR: risk-adjusted mortality rate LVH: low-volume hospital HVH: high-volume hospital DSS: disease-specific survival HR: hazards ratio LVP: low-volume physician HVP: high-volume physician MRP: medium-volume physician LAR: low anterior resection NS: not specified 29 29

30 CANCER MISCELLANEOUS 30 Study Population Time Patient # MD # Hospital Unit of Primary Risk Definition Volume: Score period # analysis outcome adjustment of low Outcomes results data source volume Hannan All 1994– 3711 1114 207 MD Inpt Admin MD: 1–2 Risk-adjusted increase in rate 10 in press NY 1997 Hosp death Hosp: 1–15 for lowest- relative to highest- Gastrectomy Both volume quartile; Hosp: 7.1% for cancer Surgeon: 5.7%; No MD effect when hosp volume controlled Glasgow All CA 1990– 507 NS 138 Hosp Inpt Admin Low: < 2 Risk-adjusted mortality rate: 6 1999 Hepatic 1994 death high: > 16 Low: 22.7 resections High: 9.4% for cancer Gordon All 1989– 938; NS 51 Hosp Inpt Admin < 11 Biliary tract anastomosis: 6 1999 Maryland 1997 705; death Measured adjusted RR = 5.3 Biliary tract 293 vol of 6 Gastrectomy: no relationship; anastomosis, complex Hepatic lobectomy: adjusted gastrectomy, GI RR = 4.7; 6 GI procedures: hepatic procedures Benign: no relationship lobectomy Malignant: adjusted RR = 5.2 (benign and malignant) Begg Medicare/ 1984– 1592; NS 250+ Hosp 30 day Clinical Low: < 1–5 Unadjusted 30 day mortality: 7 1998 US Pelvic 1993 801 death high: > 11 Pelvic: 3.7 vs. 1.5% exenteration, Hepatic: 5.4 vs. 1.7% hepatic resection Abbreviations: LVP: low-volume physician HVP: high-volume physician NS: not specified LVH: low-volume hospital HVH: high-volume hospital

APPENDIX A 31 REFERENCES Begg CB, Cramer LD, Hoskins WJ, Brennan MF. Impact of hospital volume on operative mortality for major cancer surgery. JAMA. 1998;280(20):1747– 51. Birkmeyer JD, Finlayson SR, Tosteson AN, Sharp SM, Warshaw AL, Fisher ES. Effect of hospital volume on in-hospital mortality with pancreaticoduo- denectomy. Surgery. 1999b;125(3):250–6. Birkmeyer JD, Warshaw AL, Finlayson SR, Grove MR, Tosteson AN. Relation- ship between hospital volume and late survival after pancreaticoduodenec- tomy. Surgery. 1999a;126(2):178–83. Glasgow RE, Mulvihill SJ. Hospital volume influences outcome in patients un- dergoing pancreatic resection for cancer. Western Journal of Medicine. 1996;165(5):294–300. Glasgow RE, Showstack JA, Katz PP, Corvera CU, Warren RS, Mulvihill SJ. The relationship between hospital volume and outcomes of hepatic resec- tion for hepatocellular carcinoma. Arch Surg. 1999;134(1):30–5. Gordon TA, Bowman HM, Bass EB, et al. Complex gastrointestinal surgery: Impact of provider experience on clinical and economic outcomes. J Am Coll Surg. 1999;189(1):46–56. Gordon TA, Burleyson GP, Tielsch JM, Cameron JL. The effects of regionali- zation on cost and outcome for one general high-risk surgical procedure. Annals of Surgery. 1995;221(1):43–9. Hannan E. The influence of hospital and surgeon volume on mortality for com- mon cancer procedures. Surgery, in press. Harmon JW, Tang DG, Gordon TA, et al. Hospital volume can serve as a surro- gate for surgeon volume for achieving excellent outcomes in colorectal re- section. Ann Surg. 1999;230(3):404–11; discussion 411–3. Imperato PJ, Nenner RP, Starr HA, Will TO, Rosenberg CR, Dearie MB. The effects of regionalization on clinical outcomes for a high risk surgical pro- cedure: A study of the Whipple procedure in New York State. American Journal of Medical Quality. 1996;11(4):193–7. Lieberman MD, Kilburn H, Lindsey M, Brennan MF. Relation of perioperative deaths to hospital volume among patients undergoing pancreatic resection for malignancy. Annals of Surgery. 1995;222(5):638–45. Parry JM, Collins S, Mathers J, Scott NA, Woodman CB. Influence of volume of work on the outcome of treatment for patients with colorectal cancer. Br J Surg. 1999;86(4):475–81. Patti M, Corvera CU, Glasgow RE, Way LW. A hospital’s annual rate of esophagectomy influences the operative mortality rate. Journal of Gastro- intestinal Surgery. 1998;2:186–92. Porter GA, Soskolne CL, Yakimets WW, Newman SC. Surgeon-related factors and outcome in rectal cancer. Ann Surg. 1998;227(2):157–67. Romano PS, Mark DH. Patient and hospital characteristics related to in-hospital mortality after lung cancer resection. Chest. 1992;101(5):1332–7. Roohan PJ, Bickell NA, Baptiste MS, Therriault GD, Ferrara EP, Siu AL. Hos- pital volume differences and five-year survival from breast cancer. Ameri- can Journal of Public Health. 1998;88(3):454–7.

32 INTERPRETING THE VOLUME–OUTCOME RELATIONSHIP Sainsbury R, Haward B, Rider L, Johnston C, Round C. Influence of clinician workload and patterns of treatment on survival from breast cancer. Lancet. 1995;345(8960):1265–70. Simunovic M, To T, Theriault M, Langer B. Relation between hospital surgical volume and outcome for pancreatic resection for neoplasm in a publicly funded health care system. CMAJ. 1999;160(5):643–8. Sosa JA, Bowman HM, Gordon TA, et al. Importance of hospital volume in the overall management of pancreatic cancer. Annals of Surgery. 1998;228(3):429–38. Wade TP, Halaby IA, Stapleton DR, Virgo KS, Johnson FE. Population-based analysis of treatment of pancreatic cancer and Whipple resection: Depart- ment of Defense hospitals, 1989–1994. Surgery. 1996;120(4):680–5; dis- cussion 686–7.

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Interpreting the Volume-Outcome Relationship in the Context of Cancer Care is a summary of a workshop held on May 11, 2000, which brought together experts to review evidence of the relationship between volume of services and health-related outcomes for cancer and other conditions, discuss methodological issues related to the interpretation of the association between volume and outcome, assess the applicability of volume as an indicator of quality of care; and identify research needed to better understand the volume--outcome relationship and its application to quality improvement.

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