title: Recruitment and retention strategies and the examination of attrition bias in a randomised controlled trial in children's centres serving families in disadvantaged areas of England.
abstract: BACKGROUND
  Failure to retain participants in randomised controlled trials and longitudinal studies can cause significant methodological problems. We report the recruitment and retention strategies of a randomised controlled trial to promote fire-related injury prevention in families with pre-school children attending children's centres in disadvantaged areas in England.
  
  
  METHODS
  Thirty-six children's centres were cluster randomised into one of three arms of a 12-month fire-related injury prevention trial. Two arms delivered safety interventions and there was one control arm. Retention rates compared the numbers of participants responding to the 12-month questionnaire to the number recruited to the trial. Multivariable random effects logistic regression was used to explore factors independently associated with participant retention.
  
  
  RESULTS
  The trial exceeded its required sample size through the use of multiple recruitment strategies. All children's centres remained in the study, despite increased reorganisation. Parent retention was 68% at 12 months, ranging from 65% to 70% across trial arms and from 62% to 74% across trial sites. There was no significant difference in the rates of retention between trial arms (p = 0.58) or between trial sites (p = 0.16). Retention was significantly lower amongst mothers aged 16-25 years than older mothers [adjusted odds ratio (AOR) 0.57, 95% CI 0.41, 0.78], those living in non-owner occupied accommodation than in owner occupied accommodation (AOR 0.53, 95% CI 0.38, 0.73) and those living in more disadvantaged areas (most versus least disadvantaged quintiles AOR 0.50, 95% CI 0.30, 0.82).
  
  
  CONCLUSIONS
  Studies recruiting disadvantaged populations should measure and report attrition by socioeconomic factors to enable determination of the extent of attrition bias and estimation of its potential impact on findings. Where differential attrition is anticipated, consideration should be given to over-sampling during recruitment and targeted and more intensive strategies of participant retention in these sub-groups. In transient populations collection of multiple sources of contact information at recruitment and throughout the study may aid retention.
  
  
  BACKGROUND
  Clinicaltrials.gov identifier: NCT01452191 ; Date of registration: 10 October 2011, ISRCTN65067450.
authors.affiliation: Institute of Health & Society, Baddiley-Clark Building, Newcastle University, Richardson Road, Newcastle upon Tyne, NE2 4AX, UK. paul.hindmarch@nuth.nhs.uk.
authors.forename: Paul
authors.initials: P
authors.lastname: Hindmarch
authors.affiliation: Institute of Health & Society, Baddiley-Clark Building, Newcastle University, Richardson Road, Newcastle upon Tyne, NE2 4AX, UK. adrian.hawkins@nuth.nhs.uk.
authors.forename: Adrian
authors.initials: A
authors.lastname: Hawkins
authors.affiliation: Institute of Health & Society, Baddiley-Clark Building, Newcastle University, Richardson Road, Newcastle upon Tyne, NE2 4AX, UK. elaine.mccoll@newcastle.ac.uk.
authors.forename: Elaine
authors.initials: E
authors.lastname: McColl
authors.affiliation: Child Accident Prevention Trust, Canterbury Court (1.09), 1-3 Brixton Road, London, SW9 6DE, UK. mhayes@capt.org.uk.
authors.forename: Mike
authors.initials: M
authors.lastname: Hayes
authors.affiliation: Clinical Research & Trials Unit, Norfolk and Norwich University Hospital NHS Foundation Trust, Norwich, NR4 7UY, UK. gosia.majsak-newmann@nnuh.nhs.uk.
authors.forename: Gosia
authors.initials: G
authors.lastname: Majsak-Newman
authors.affiliation: Division of Primary Care, School of Medicine, Floor 13, Tower Building, University Park, Nottingham, NG7 2RD, UK. joanne.ablewhite@nottingham.ac.uk.
authors.forename: Joanne
authors.initials: J
authors.lastname: Ablewhite
authors.affiliation: Faculty of Health and Applied Sciences, University of the West of England, Bristol, BS16 1QY, UK. toity.deave@uwe.ac.uk.
authors.forename: Toity
authors.initials: T
authors.lastname: Deave
authors.affiliation: Division of Primary Care, School of Medicine, Floor 13, Tower Building, University Park, Nottingham, NG7 2RD, UK. denise.kendrick@nottingham.ac.uk.
authors.forename: Denise
authors.initials: D
authors.lastname: Kendrick
mesh_terms: D015982:Bias; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D010290:Parents; D018579:Patient Selection; D016032:Randomized Controlled Trials as Topic; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires