title: Effects of study design and trends for EVAR versus OSR.
abstract: OBJECTIVE
  To investigate if study design factors such as randomization, multi-center versus single center evidence, institutional surgical volume, and patient selection affect the outcomes for endovascular repair (EVAR) versus open surgical repair (OSR). Finally, we investigate trends over time in EVAR versus OSR outcomes.
  
  
  METHODS
  Search strategies for comparative studies were performed individually for: OVID's MEDLINE, EMBASE, CINAHL, HAPI, and Evidence Based Medicine (EBM) Reviews (including Cochrane DSR, ACP Journal Club, DARE and CCTR), limited to 1990 and November 2006.
  
  
  RESULTS
  Identified literature: 84 comparative studies pertaining to 57,645 patients. These include 4 randomized controlled trials (RCTs), plus 2 RCTs with long-term follow-up. The other 78 comparative studies were nonrandomized with 75 reporting perioperative outcomes, of which 16 were multi-center, and 59 single-center studies. Of the single-center studies 31 were low-volume and 28 were high-volume centers. In addition, 5 studies had all patients anatomically eligible for EVAR, and 8 studies included high-risk patients only. Finally, 25 long term observational studies reported outcomes up to 3 years.
  
  
  RESULTS
  Lower perioperative mortality and rates of complications for EVAR versus OSR varied across study designs and patient populations. EVAR adverse outcomes have decreased in recent times.
  
  
  CONCLUSIONS
  EVAR highlights the problem of performing meta-analysis when the experience evolves over time.
authors.affiliation: Program for the Assessment of Technology in Health (PATH) Research Institute, Department of Clinical Epidemiology and Biostatistics, London Health Sciences Center, London, Ontario, Canada. hopkinr@mcmaster.ca
authors.forename: Robert
authors.initials: R
authors.lastname: Hopkins
authors.forename: James
authors.initials: J
authors.lastname: Bowen
authors.forename: Kaitryn
authors.initials: K
authors.lastname: Campbell
authors.forename: Gord
authors.initials: G
authors.lastname: Blackhouse
authors.forename: Guy
authors.initials: G
authors.lastname: De Rose
authors.forename: Teresa
authors.initials: T
authors.lastname: Novick
authors.forename: Daria
authors.initials: D
authors.lastname: O'Reilly
authors.forename: Ron
authors.initials: R
authors.lastname: Goeree
authors.forename: Jean-Eric
authors.initials: JE
authors.lastname: Tarride
mesh_terms: D017544:Aortic Aneurysm, Abdominal / Q000401:mortality / Q000601:surgery*; D001807:Blood Vessel Prosthesis; D019917:Blood Vessel Prosthesis Implantation / Q000009:adverse effects / Q000295:instrumentation / Q000401:mortality; D002986:Clinical Trials as Topic / Q000379:methods*; D005260:Female; D006801:Humans; D007511:Ischemia / Q000209:etiology; D008297:Male; D019060:Minimally Invasive Surgical Procedures; D016017:Odds Ratio; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012107:Research Design; D018570:Risk Assessment; D015607:Stents; D013997:Time Factors; D016896:Treatment Outcome