title: Assessing the quality of the volume-outcome relationship in uro-oncology.
abstract: OBJECTIVE
  To assess systematically the quality of evidence for the volume-outcome relationship in uro-oncology, and thus facilitate the formulating of health policy within this speciality, as 'Implementation of Improving Outcome Guidance' has led to centralization of uro-oncology based on published studies that have supported a 'higher volume-better outcome' relationship, but improved awareness of methodological drawbacks in health service research has questioned the strength of this proposed volume-outcome relationship.
  
  
  METHODS
  We systematically searched previous relevant reports and extracted all articles from 1980 onwards assessing the volume-outcome relationship for cystectomy, prostatectomy and nephrectomy at the institution and/or surgeon level. Studies were assessed for their methodological quality using a previously validated rating system. Where possible, meta-analytical methods were used to calculate overall differences in outcome measures between low and high volume healthcare providers.
  
  
  RESULTS
  In all, 22 studies were included in the final analysis; 19 of these were published in the last 5 years. Only four studies appropriately explored the effect of both the institution and surgeon volume on outcome measures. Mortality and length of stay were the most frequently measured outcomes. The median total quality scores within each of the operation types were 8.5, 9 and 8 for cystectomy, prostatectomy and nephrectomy, respectively (possible maximum score 18). Random-effects modelling showed a higher risk of mortality in low-volume institutions than in higher-volume institutions for both cystectomy and nephrectomy (odds ratio 1.88, 95% confidence interval 1.54-2.29, and 1.28, 1.10-1.49, respectively).
  
  
  CONCLUSIONS
  The methodological quality of volume-outcome research as applied to cystectomy, prostatectomy and nephrectomy is only modest at best. Accepting several limitations, pooled analysis confirms a higher-volume, lower-mortality relationship for cystectomy and nephrectomy. Future research should focus on the development of a quality framework with a validated scoring system for the bench-marking of data to improve validity and facilitate rational policy-making within the speciality of uro-oncology.
authors.affiliation: Department of Urology, St Mary's Hospital Campus, Imperial College Healthcare NHS Trust, London, UK. e.mayer@imperial.ac.uk
authors.forename: Erik K
authors.initials: EK
authors.lastname: Mayer
authors.forename: Sanjay
authors.initials: S
authors.lastname: Purkayastha
authors.forename: Thanos
authors.initials: T
authors.lastname: Athanasiou
authors.forename: Ara
authors.initials: A
authors.lastname: Darzi
authors.forename: Justin A
authors.initials: JA
authors.lastname: Vale
mesh_terms: D015653:Cystectomy / Q000592:standards* / Q000706:statistics & numerical data; D006801:Humans; D009392:Nephrectomy / Q000592:standards* / Q000706:statistics & numerical data; D010043:Outcome and Process Assessment, Health Care; D011468:Prostatectomy / Q000592:standards* / Q000706:statistics & numerical data; D012307:Risk Factors; D014571:Urologic Neoplasms / Q000601:surgery*; D016526:Workload