title: A randomised controlled trial to compare opt-in and opt-out parental consent for childhood vaccine safety surveillance using data linkage: study protocol.
abstract: BACKGROUND
  The Vaccine Assessment using Linked Data (VALiD) trial compared opt-in and opt-out parental consent for a population-based childhood vaccine safety surveillance program using data linkage. A subsequent telephone interview of all households enrolled in the trial elicited parental intent regarding the return or non-return of reply forms for opt-in and opt-out consent. This paper describes the rationale for the trial and provides an overview of the design and methods.
  
  
  METHODS
  Single-centre, single-blind, randomised controlled trial (RCT) stratified by firstborn status. Mothers who gave birth at one tertiary South Australian hospital were randomised at six weeks post-partum to receive an opt-in or opt-out reply form, along with information explaining data linkage. The primary outcome at 10 weeks post-partum was parental participation in each arm, as indicated by the respective return or non-return of a reply form (or via telephone or email response). A subsequent telephone interview at 10 weeks post-partum elicited parental intent regarding the return or non-return of the reply form, and attitudes and knowledge about data linkage, vaccine safety, consent preferences and vaccination practices. Enrolment began in July 2009 and 1,129 households were recruited in a three-month period. Analysis has not yet been undertaken. The participation rate and selection bias for each method of consent will be compared when the data are analysed.
  
  
  CONCLUSIONS
  The VALiD RCT represents the first trial of opt-in versus opt-out consent for a data linkage study that assesses consent preferences and intent compared with actual opting in or opting out behaviour, and socioeconomic factors. The limitations to generalisability are discussed.
  
  
  BACKGROUND
  Australian New Zealand Clinical Trials Registry ACTRN12610000332022.
authors.affiliation: Discipline of Public Health, The University of Adelaide, Adelaide, South Australia. Jesia.Berry@adelaide.edu.au
authors.forename: Jesia G
authors.initials: JG
authors.lastname: Berry
authors.forename: Philip
authors.initials: P
authors.lastname: Ryan
authors.forename: Annette J
authors.initials: AJ
authors.lastname: Braunack-Mayer
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Duszynski
authors.forename: Vicki
authors.initials: V
authors.lastname: Xafis
authors.forename: Michael S
authors.initials: MS
authors.lastname: Gold
mesh_terms: D003625:Data Collection / Q000706:statistics & numerical data; D015438:Health Behavior; D019538:Health Care Surveys; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D017589:Immunization Programs; D007115:Immunization Schedule; D007223:Infant; D008498:Medical Record Linkage; D033282:Parental Consent / Q000706:statistics & numerical data; D010290:Parents / Q000523:psychology*; D011159:Population Surveillance; D011358:Product Surveillance, Postmarketing / Q000706:statistics & numerical data; D012107:Research Design; D016037:Single-Blind Method; D012959:Socioeconomic Factors; D013021:South Australia / Q000453:epidemiology; D014612:Vaccines / Q000009:adverse effects*
chemical_list: D014612:Vaccines