Gasche, C, Scholmerich, J, Brynskov, J, et al. A simple classification of Crohn's disease: Report of the Working Party for the World Congresses of Gastroenterology, Vienna 1998. Inflamm Bowel Dis 2000;6:8–15.
Bewtra, M, Su, C, Lewis, JD. Trends in hospitalization rates for inflammatory bowel disease in the United States. Clin Gastroenterol Hepatol 2007;5:597–601.
Jess, T, Riis, L, Vind, I, et al. Changes in clinical characteristics, course, and prognosis of inflammatory bowel disease during the last 5 decades: A population-based study from Copenhagen, Denmark. Inflamm Bowel Dis 2007;13:481–489.
Vind, I, Riis, L, Jess, T, et al. Increasing incidences of inflammatory bowel disease and decreasing surgery rates in Copenhagen City and County, 2003–2005: A population-based study from the Danish Crohn colitis database. Am J Gastroenterol 2006;101:1274–1282.
Bassi, A, Dodd, S, Williamson, P, et al. Cost of illness of inflammatory bowel disease in the UK: A single centre retrospective study. Gut 2004;53:1471–1478.
Bernstein, CN, Papineau, N, Zajaczkowski, J, et al. Direct hospital costs for patients with inflammatory bowel disease in a Canadian tertiary care university hospital. Am J Gastroenterol 2000;95:677–683.
Feagan, BG, Vreeland, MG, Larson, LR, et al. Annual cost of care for Crohn's disease: A payor perspective. Am J Gastroenterol 2000;95:1955–1960.
Odes, S, Vardi, H, Friger, M, et al. Cost analysis and cost determinants in a European inflammatory bowel disease inception cohort with 10 years of follow-up evaluation. Gastroenterology 2006;131:719–728.
Bach, PB, Cramer, LD, Schrag, D, et al. The influence of hospital volume on survival after resection for lung cancer. N Engl J Med 2001;345:181–188.
Gilligan, MA, Neuner, J, Zhang, X, et al. Relationship between number of breast cancer operations performed and 5-year survival after treatment for early-stage breast cancer. Am J Public Health 2007;97:539–544.
Meyerhardt, JA, Catalano, PJ, Schrag, D, et al. Association of hospital procedure volume and outcomes in patients with colon cancer at high risk for recurrence. Ann Intern Med 2003;139:649–657.
Schrag, D, Cramer, LD, Bach, PB, et al. Influence of hospital procedure volume on outcomes following surgery for colon cancer. JAMA 2000;284:3028–3035.
Birkmeyer, JD, Stukel, TA, Siewers, AE, et al. Surgeon volume and operative mortality in the United States. N Engl J Med 2003;349:2117–2127.
Chowdhury, MM, Dagash, H, Pierro, A. A systematic review of the impact of volume of surgery and specialization on patient outcome. Br J Surg 2007;94:145–161.
Cowan, JA, Jr, Dimick, JB, Henke, PK, et al. Surgical treatment of intact thoracoabdominal aortic aneurysms in the United States: Hospital and surgeon volume-related outcomes. J Vasc Surg 2003;37:1169–1174.
Halm, EA, Lee, C, Chassin, MR. Is volume related to outcome in health care? A systematic review and methodologic critique of the literature. Ann Intern Med 2002;137:511–520.
Lin, HC, Xirasagar, S, Lee, HC, et al. Hospital volume and inpatient mortality after cancer-related gastrointestinal resections: The experience of an Asian country. Ann Surg Oncol 2006;13:1182–1188.
Smith, JK, McPhee, JT, Hill, JS, et al. National outcomes after gastric resection for neoplasm. Arch Surg 2007;142:387–393.
Dimick, JB, Cowan, JA, Jr, Colletti, LM, et al. Hospital teaching status and outcomes of complex surgical procedures in the United States. Arch Surg 2004;139:137–141.
Dimick, JB, Cowan, JA, Jr, Henke, PK, et al. Hospital volume-related differences in aorto-bifemoral bypass operative mortality in the United States. J Vasc Surg 2003;37:970–975.
Dimick, JB, Cowan, JA, Jr, Upchurch, GR, Jr, et al. Hospital volume and surgical outcomes for elderly patients with colorectal cancer in the United States. J Surg Res 2003;114:50–56.
Finlayson, EV, Goodney, PP, Birkmeyer, JD. Hospital volume and operative mortality in cancer surgery: A national study. Arch Surg 2003;138:721–725; discussion 726.
Rathore, SS, Epstein, AJ, Volpp, KG, et al. Hospital coronary artery bypass graft surgery volume and patient mortality, 1998–2000. Ann Surg 2004;239:110–117.
Chappel, AR, Zuckerman, RS, Finlayson, SR. Small rural hospitals and high-risk operations: How would regionalization affect surgical volume and hospital revenue? J Am Coll Surg 2006;203:599–604.
Grumbach, K, Anderson, GM, Luft, HS, et al. Regionalization of cardiac surgery in the United States and Canada. Geographic access, choice, and outcomes. JAMA 1995;274:1282–1288.
Jollis, JG, Peterson, ED, DeLong, ER, et al. The relation between the volume of coronary angioplasty procedures at hospitals treating Medicare beneficiaries and short-term mortality. N Engl J Med 1994;331:1625–1629.
Rohrer, JE, Vaughan, MS, Wenzel, RP. Regionalization of tertiary care: Impact of safe cardiovascular volumes in Iowa. Health Serv Manage Res 1997;10:1–6.
Glance, LG, Li, Y, Osler, TM, et al. Impact of patient volume on the mortality rate of adult intensive care unit patients. Crit Care Med 2006;34:1925–1934.
Kahn, JM, Goss, CH, Heagerty, PJ, et al. Hospital volume and the outcomes of mechanical ventilation. N Engl J Med 2006;355:41–50.
Needham, DM, Bronskill, SE, Rothwell, DM, et al. Hospital volume and mortality for mechanical ventilation of medical and surgical patients: A population-based analysis using administrative data. Crit Care Med 2006;34:2349–2354.
HCUP Nationwide Inpatient Sample (NIS). Healthcare Cost and Utilization Project (HCUP). 2004. Agency for Healthcare Research and Quality, Rockville, MD. Available at: http://www.hcup-us.ahrq.gov/nisoverview.jsp. Accessed December 23, 2007.
Steiner, C, Elixhauser, A, Schnaier, J. The healthcare cost and utilization project: An overview. Eff Clin Pract 2002;5:143–151.
Whalen, D, Houchens, R, Elixhauser, A. 2004. HCUP Nationwide Inpatient Sample (NIS) Comparison Report. HCUP Methods Series Report # 2007–03. U.S. Agency for Healthcare Research and Quality. Available at: http://www.hcup-us.ahrq.gov/reports/methods.jsp. Accessed February 2, 2007.
Elixhauser, A, Steiner, C, Fraser, I. Volume thresholds and hospital characteristics in the United States. Health Aff (Millwood) 2003;22:167–177.
Nguyen, GC, Bayless, TM, Powe, NR, et al. Race and health insurance are predictors of hospitalized Crohn's disease patients undergoing bowel resection. Inflamm Bowel Dis 2007;13:1408–1416.
Charlson, ME, Pompei, P, Ales, KL, et al. A new method of classifying prognostic comorbidity in longitudinal studies: Development and validation. J Chronic Dis 1987;40:373–383.
Deyo, RA, Cherkin, DC, Ciol, MA. Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases. J Clin Epidemiol 1992;45:613–619.
Bernstein, CN, Nabalamba, A. Hospitalization, surgery, and readmission rates of IBD in Canada: A population-based study. Am J Gastroenterol 2006;101:110–118.
Rosenthal, GE, Harper, DL, Quinn, LM, et al. Severity-adjusted mortality and length of stay in teaching and nonteaching hospitals. Results of a regional study. JAMA 1997;278:485–490.
Joffe, MM, Rosenbaum, PR. Invited commentary: Propensity scores. Am J Epidemiol 1999;150:327–333.
Rubin, DB. Estimating causal effects from large data sets using propensity scores. Ann Intern Med 1997;127:757–763.
Kaplan, GG, McCarthy, EP, Ayanian, JZ, et al. Impact of hospital volume on postoperative morbidity and mortality following a colectomy for ulcerative colitis. Gastroenterology 2008;134:680–687.
Varadarajulu, S, Kilgore, ML, Wilcox, CM, et al. Relationship among hospital ERCP volume, length of stay, and technical outcomes. Gastrointest Endosc 2006;64:338–347.
Shaheen, NJ, Hansen, RA, Morgan, DR, et al. The burden of gastrointestinal and liver diseases, 2006. Am J Gastroenterol 2006;101:2128–2138.
Henebiens, M, Van Den Broek, TA, Vahl, AC, et al. Relation between hospital volume and outcome of elective surgery for abdominal aortic aneurysm: A systematic review. Eur J Vasc Endovasc Surg 2007;33:285–292.
Esrailian, E, Spiegel, BM, Targownik, LE, et al. Differences in the management of Crohn's disease among experts and community providers, based on a national survey of sample case vignettes. Aliment Pharmacol Ther 2007;26:1005–1018.
Kappelman, MD, Bousvaros, A, Hyams, J, et al. Intercenter variation in initial management of children with Crohn's disease. Inflamm Bowel Dis 2007;13:890–895.
Mawdsley, JE, Irving, PM, Makins, RJ, et al. Optimizing quality of outpatient care for patients with inflammatory bowel disease: The importance of specialist clinics. Eur J Gastroenterol Hepatol 2006;18:249–253.
Feagan, BG. Medical management of ulcerative colitis in 2006: What's on the horizon? Am J Gastroenterol 2007;102:S7–S13.
Zankel, E, Rogler, G, Andus, T, et al. Crohn's disease patient characteristics in a tertiary referral center: Comparison with patients from a population-based cohort. Eur J Gastroenterol Hepatol 2005;17:395–401.
Finlayson, SR. The volume-outcome debate revisited. Am Surg 2006;72:1038–1042; discussion 1061–9, 1133–48.
Thiemann, DR, Coresh, J, Oetgen, WJ, et al. The association between hospital volume and survival after acute myocardial infarction in elderly patients. N Engl J Med 1999;340:1640–1648.