title: Elicitation of expert prior opinion: application to the MYPAN trial in childhood polyarteritis nodosa.
abstract: OBJECTIVE
  Definitive sample sizes for clinical trials in rare diseases are usually infeasible. Bayesian methodology can be used to maximise what is learnt from clinical trials in these circumstances. We elicited expert prior opinion for a future Bayesian randomised controlled trial for a rare inflammatory paediatric disease, polyarteritis nodosa (MYPAN, Mycophenolate mofetil for polyarteritis nodosa).
  
  
  METHODS
  A Bayesian prior elicitation meeting was convened. Opinion was sought on the probability that a patient in the MYPAN trial treated with cyclophosphamide would achieve disease remission within 6-months, and on the relative efficacies of mycophenolate mofetil and cyclophosphamide. Expert opinion was combined with previously unseen data from a recently completed randomised controlled trial in ANCA associated vasculitis.
  
  
  RESULTS
  A pan-European group of fifteen experts participated in the elicitation meeting. Consensus expert prior opinion was that the most likely rates of disease remission within 6 months on cyclophosphamide or mycophenolate mofetil were 74% and 71%, respectively. This prior opinion will now be taken forward and will be modified to formulate a Bayesian posterior opinion once the MYPAN trial data from 40 patients randomised 1:1 to either CYC or MMF become available.
  
  
  CONCLUSIONS
  We suggest that the methodological template we propose could be applied to trial design for other rare diseases.
authors.affiliation: Department of Mathematics and Statistics, Lancaster University, Lancaster, United Kingdom.
authors.forename: Lisa V
authors.initials: LV
authors.lastname: Hampson
authors.affiliation: Department of Mathematics and Statistics, Lancaster University, Lancaster, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Whitehead
authors.affiliation: Department of Rheumatology, UCL Institute of Child Health, London, United Kingdom.
authors.forename: Despina
authors.initials: D
authors.lastname: Eleftheriou
authors.affiliation: MRC North West Hub for Trials Methodology Research, Department of Biostatistics, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Catrin
authors.initials: C
authors.lastname: Tudur-Smith
authors.affiliation: Department of Renal Medicine, Addenbrooke's Hospital, Hills Road, Cambridge, United Kingdom.
authors.forename: Rachel
authors.initials: R
authors.lastname: Jones
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Jayne
authors.affiliation: Medicines for Children Research Network Clinical Trials Unit, University of Liverpool, Alder Hey Children's NHS Foundation Trust, Liverpool, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Hickey
authors.affiliation: Department of Women's & Children's Health, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Beresford
authors.affiliation: Division of Rheumatology, Department of Paediatric Medicine, IRCCS Bambino Gesù Children Hospital, Piazza Sant'Onofrio 4, 00165, Rome, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Bracaglia
authors.affiliation: Oporto Medical School, Integrated Hospital S. João, Porto, Portugal.
authors.forename: Afonso
authors.initials: A
authors.lastname: Caldas
authors.affiliation: AOU Meyer, Viale Pieraccini 24, 50139, Florence, Italy.
authors.forename: Rolando
authors.initials: R
authors.lastname: Cimaz
authors.affiliation: Department of Pediatric Rheumatology and Nephrology, Universitary Hospital Ghent, Ghent, Belgium.
authors.forename: Joke
authors.initials: J
authors.lastname: Dehoorne
authors.affiliation: Department of Paediatrics and Adolescent Medicine, Charles University in Prague, 1st Faculty of Medicine and General University Hospital, Prague, Czech Republic.
authors.forename: Pavla
authors.initials: P
authors.lastname: Dolezalova
authors.affiliation: Great North Children's Hospital, Newcastle upon Tyne, United Kingdom.
authors.forename: Mark
authors.initials: M
authors.lastname: Friswell
authors.affiliation: Department of Paediatric Rheumatology, University of Zagreb School of Medicine, University Hospital Centre Zagreb, Zagreb, Croatia.
authors.forename: Marija
authors.initials: M
authors.lastname: Jelusic
authors.affiliation: Department of Paediatric Nephrology, Great Ormond Street Hospital for Children NHS Foundation Trust, Great Ormond Street, London, WC1N 3JH, United Kingdom.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Marks
authors.affiliation: Department of Paediatric Rheumatology, Yorkhill Hospital, Glasgow, United Kingdom.
authors.forename: Neil
authors.initials: N
authors.lastname: Martin
authors.affiliation: Sheffield Children's Hospital NHS Foundation Trust, Sheffield, United Kingdom.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: McMahon
authors.affiliation: Hospital for Children and Adolescents, University Hospital of Cologne, Cologne, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Peitz
authors.affiliation: Wilhelmina Children's Hospital, University Medical Centre, Utrecht, Netherlands.
authors.forename: Annet
authors.initials: A
authors.lastname: van Royen-Kerkhof
authors.affiliation: Department of Pediatric Nephrology and Rheumatology, Gazi University Hospital, Ankara, Turkey.
authors.forename: Oguz
authors.initials: O
authors.lastname: Soylemezoglu
authors.affiliation: Department of Rheumatology, UCL Institute of Child Health, London, United Kingdom.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Brogan
mesh_terms: D001499:Bayes Theorem; D002648:Child; D002986:Clinical Trials as Topic; D003520:Cyclophosphamide / Q000627:therapeutic use*; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use*; D009173:Mycophenolic Acid / Q000031:analogs & derivatives* / Q000627:therapeutic use; D010488:Polyarteritis Nodosa / Q000188:drug therapy*; D016032:Randomized Controlled Trials as Topic; D035583:Rare Diseases / Q000188:drug therapy; D016896:Treatment Outcome
chemical_list: D007166:Immunosuppressive Agents; D003520:Cyclophosphamide; D009173:Mycophenolic Acid
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