title: Predictors of non-response in a UK-wide cohort study of children's accelerometer-determined physical activity using postal methods.
abstract: OBJECTIVE
  To investigate the biological, social, behavioural and environmental factors associated with non-consent, and non-return of reliable accelerometer data (≥2 days lasting ≥10 h/day), in a UK-wide postal study of children's activity.
  
  
  METHODS
  Nationally representative prospective cohort study.
  
  
  METHODS
  Children born across the UK, between 2000 and 2002.
  
  
  METHODS
  13 681 7 to 8-year-old singleton children who were invited to wear an accelerometer on their right hip for 7 consecutive days. Consenting families were posted an Actigraph GT1M accelerometer and asked to return it by post.
  
  
  METHODS
  Study consent and reliable accelerometer data acquisition.
  
  
  RESULTS
  Consent was obtained for 12 872 (94.5%) interviewed singletons, of whom 6497 (50.5%) returned reliable accelerometer data. Consent was less likely for children with a limiting illness or disability, children who did not have people smoking near them, children who had access to a garden, and those who lived in Northern Ireland. From those who consented, reliable accelerometer data were less likely to be acquired from children who: were boys; overweight/obese; of white, mixed or 'other' ethnicity; had an illness or disability limiting daily activity; whose mothers did not have a degree; who lived in rented accommodation; who exercised once a week or less; who had been breastfed; were from disadvantaged wards; had younger mothers or lone mothers; or were from households with just one, or more than three children.
  
  
  CONCLUSIONS
  Studies need to encourage consent and reliable data return in the wide range of groups we have identified to improve response and reduce non-response bias. Additional efforts targeted at such children should increase study consent and data acquisition while also reducing non-response bias. Adjustment must be made for missing data that account for missing data as a non-random event.
authors: MRC Centre of Epidemiology for Child Health, UCL Institute of Child Health, London, UK.
authors: Carly
authors: C
authors: Rich
authors: Mario
authors: M
authors: Cortina-Borja
authors: Carol
authors: C
authors: Dezateux
authors: Marco
authors: M
authors: Geraci
authors: Francesco
authors: F
authors: Sera
authors: Lisa
authors: L
authors: Calderwood
authors: Heather
authors: H
authors: Joshi
authors: Lucy J
authors: LJ
authors: Griffiths