title: The account for provider and center effects in multicenter interventional and surgical randomized controlled trials is in need of improvement: a review.
abstract: OBJECTIVE
  To systematically review the account of center and provider effects in large surgical and interventional randomized controlled trials.
  
  
  METHODS
  A systematic review of multicenter interventional randomized trials of 200+ patients. The search included Medline from 1 January 2000 through 11 October 2005 and a hand search of the bibliographies of retrieved articles. One author abstracted all data using standardized abstraction forms; a second reviewer assessed a random sample of reports as quality-assurance procedure.
  
  
  RESULTS
  Sixty-eight reports met inclusion criteria. The trials predominantly reported on cardiology (n=23, 34%). The number of participating providers was reported in 11 trials (16%). Both the performed control and performed interventional procedures were described in 43 trials (63%). The use of stratified random allocation on center was reported in 26 trials (38%) and on provider in 6 trials (9%). The analysis was adjusted for center in four trials (6%) and for provider in three trials (4%).
  
  
  CONCLUSIONS
  Only few trials account for center or provider effect in the design and analysis. Authors and journal editors could play an important role in improving the reporting of trials.
authors.affiliation: INSERM U717; Departement de Biostatistique et Informatique Médicale, Hôpital Saint-Louis-Université Paris 7, Paris, France. djmbiau@yahoo.fr
authors.forename: David J
authors.initials: DJ
authors.lastname: Biau
authors.forename: Raphaël
authors.initials: R
authors.lastname: Porcher
authors.forename: Isabelle
authors.initials: I
authors.lastname: Boutron
mesh_terms: D006801:Humans; D015337:Multicenter Studies as Topic / Q000379:methods* / Q000592:standards; D011785:Quality Assurance, Health Care; D016032:Randomized Controlled Trials as Topic / Q000379:methods* / Q000592:standards; D012107:Research Design; D013514:Surgical Procedures, Operative; D016896:Treatment Outcome