title: A randomised controlled trial to compare opt-in and opt-out parental consent for childhood vaccine safety surveillance using data linkage.
abstract: BACKGROUND
  No consent for health and medical research is appropriate when the criteria for a waiver of consent are met, yet some ethics committees and data custodians still require informed consent.
  
  
  METHODS
  A single-blind parallel-group randomised controlled trial: 1129 families of children born at a South Australian hospital were sent information explaining data linkage of childhood immunisation and hospital records for vaccine safety surveillance with 4 weeks to opt in or opt out by reply form, telephone or email. A subsequent telephone interview gauged the intent of 1026 parents (91%) in relation to their actions and the sociodemographic differences between participants and non-participants in each arm.
  
  
  RESULTS
  The participation rate was 21% (n=120/564) in the opt-in arm and 96% (n=540/565) in the opt-out arm (χ(2) (1 df) = 567.7, p<0.001). Participants in the opt-in arm were more likely than non-participants to be older, married/de facto, university educated and of higher socioeconomic status. Participants in the opt-out arm were similar to non-participants, except men were more likely to opt out. Substantial proportions did not receive, understand or properly consider study invitations, and opting in or opting out behaviour was often at odds with parents' stated underlying intentions.
  
  
  CONCLUSIONS
  The opt-in approach resulted in low participation and a biased sample that would render any subsequent data linkage unfeasible, while the opt-out approach achieved high participation and a representative sample. The waiver of consent afforded under current privacy regulations for data linkage studies meeting all appropriate criteria should be granted by ethics committees, and supported by data custodians.
  
  
  BACKGROUND
  Australian New Zealand Clinical Trials Registry ACTRN12610000332022.
authors.affiliation: Discipline of Public Health, University of Adelaide, Level 6, Bice Building, Royal Adelaide Hospital, Mail Drop DX650 511, Adelaide, South Australia, 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: Michael S
authors.initials: MS
authors.lastname: Gold
authors.forename: Annette J
authors.initials: AJ
authors.lastname: Braunack-Mayer
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Duszynski
mesh_terms: D000328:Adult; D016907:Adverse Drug Reaction Reporting Systems; D001315:Australia; D003625:Data Collection; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D033282:Parental Consent; D018579:Patient Selection; D011159:Population Surveillance; D012449:Safety; D016037:Single-Blind Method; D014612:Vaccines / Q000009:adverse effects*
chemical_list: D014612:Vaccines