title: A randomised controlled trial comparing opt-in and opt-out home visits for tracing lost participants in a prospective birth cohort study.
abstract: BACKGROUND
  Attrition is an important problem in cohort studies. Tracing cohort members who have moved or otherwise lost contact with the study is vital. There is some debate about the acceptability and relative effectiveness of opt-in versus opt-out methods of contacting cohort members to re-engage them in this context. We conducted a randomised controlled trial to compare the two approaches in terms of effectiveness (tracing to confirm address and consenting to continue in the study), cost-effectiveness and acceptability.
  
  
  METHODS
  Participants in this trial were individuals (young people and mothers) recruited to the Avon Longitudinal Study of Parents and Children (ALSPAC), who had not engaged with the study in the previous 5 years and for whom mail had been returned from their last known address. The sampling frame was restricted to those for whom database searching led to a potential new address being found in the Bristol area. 300 participants were randomly selected and assigned using stratified randomisation to the opt-in or opt-out arm. A tailored letter was sent to the potential new address, either asking participants to opt in to a home visit, or giving them the option to opt out of a home visit. Fieldworkers from Ipsos MORI conducted home visits to confirm address details.
  
  
  RESULTS
  The proportion who were traced was higher in the opt-out arm (77/150 = 51 %) than the opt-in arm (6/150 = 4 %), as was the proportion who consented to continue in ALSPAC (46/150 = 31 % v 4/150 = 3 %). The mean cost per participant was £8.14 in the opt-in arm and £71.93 in the opt-out arm. There was no evidence of a difference in acceptability between the opt-in and opt-out approaches.
  
  
  CONCLUSIONS
  Since the opt-in approach yielded very low response rates, and there were no differences in terms of acceptability, we conclude that the opt-out approach is the most effective method of tracing disengaged study members. The gains made in contacting participants must be weighed against the increase in cost using this methodology.
authors.affiliation: Department of Health and Social Science, University of the West of England, Frenchay Campus, Bristol, BS16 1QY, UK. Issy.Bray@uwe.ac.uk.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bray
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK. S.M.Noble@bristol.ac.uk.
authors.forename: Sian
authors.initials: S
authors.lastname: Noble
authors.affiliation: ALSPAC, School of Social and Community Medicine, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. A.W.Boyd@bristol.ac.uk.
authors.forename: Andy
authors.initials: A
authors.lastname: Boyd
authors.affiliation: The Ethox Centre, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Oxford, OX3 7LF, UK. lvbrown79@gmail.com.
authors.forename: Lindsey
authors.initials: L
authors.lastname: Brown
authors.affiliation: The Ethox Centre, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Oxford, OX3 7LF, UK. Pei.Tse@bristol.ac.uk.
authors.forename: Pei
authors.initials: P
authors.lastname: Hayes
authors.affiliation: ALSPAC, School of Social and Community Medicine, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. J.Malcom@bristol.ac.uk.
authors.forename: Joanne
authors.initials: J
authors.lastname: Malcolm
authors.affiliation: ALSPAC, School of Social and Community Medicine, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. Ross.Robinson@bristol.ac.uk.
authors.forename: Ross
authors.initials: R
authors.lastname: Robinson
authors.affiliation: Ipsos MORI, 79-81 Borough Road, London, SE1 1FY, UK. Rachel.Williams@ipsos.com.
authors.forename: Rachel
authors.initials: R
authors.lastname: Williams
authors.affiliation: Ipsos MORI, 79-81 Borough Road, London, SE1 1FY, UK. Kirsty.Burston@ipsos.com.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Burston
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK. John.Macleod@bristol.ac.uk.
authors.forename: John
authors.initials: J
authors.lastname: Macleod
authors.affiliation: ALSPAC, School of Social and Community Medicine, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. Lynn.Molloy@bristol.ac.uk.
authors.forename: Lynn
authors.initials: L
authors.lastname: Molloy
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK. Kate.Tilling@bristol.ac.uk.
authors.forename: Kate
authors.initials: K
authors.lastname: Tilling
mesh_terms: D000328:Adult; D002648:Child; D003362:Cost-Benefit Analysis; D005260:Female; D006699:Home Care Services / Q000191:economics / Q000706:statistics & numerical data; D006792:House Calls / Q000191:economics / Q000706:statistics & numerical data*; D006801:Humans; D008137:Longitudinal Studies; D059012:Lost to Follow-Up; D009035:Mothers; D017063:Outcome Assessment, Health Care / Q000191:economics / Q000379:methods / Q000706:statistics & numerical data; D010342:Patient Acceptance of Health Care / Q000706:statistics & numerical data*; D018579:Patient Selection; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D018401:Sample Size; D011795:Surveys and Questionnaires