title: Use of accelerometers in a large field-based study of children: protocols, design issues, and effects on precision.
abstract: BACKGROUND
  Objective methods can improve accuracy of physical activity measurement in field studies but uncertainties remain about their use.
  
  
  METHODS
  Children age 11 years from the Avon Longitudinal Study of Parents and Children (ALSPAC), were asked to wear a uni-axial accelerometer (MTI Actigraph) for 7 days.
  
  
  RESULTS
  Of 7159 children who attended for assessment, 5595 (78%) provided valid measures. The reliability coefficient for 3 days of recording was .7 and the power to detect a difference of 0.07 SDs (P<or=.05) was > 90%. Measures tended to be higher on the first day of recording (17 counts/min; 95% CI, 10-24) and if children wore the monitor for fewer days, but these differences were small. The children who provided valid measures of activity were different from those who did not, but the differences were modest.
  
  
  CONCLUSIONS
  Objective measures of physical activity can be incorporated into large longitudinal studies of children.
authors: Dept of Social Medicine, University of Bristol, UK.
authors: Calum
authors: C
authors: Mattocks
authors: Andy
authors: A
authors: Ness
authors: Sam
authors: S
authors: Leary
authors: Kate
authors: K
authors: Tilling
authors: Stephen N
authors: SN
authors: Blair
authors: Julian
authors: J
authors: Shield
authors: Kevin
authors: K
authors: Deere
authors: Joanne
authors: J
authors: Saunders
authors: Joanne
authors: J
authors: Kirkby
authors: George Davey
authors: GD
authors: Smith
authors: Jonathan
authors: J
authors: Wells
authors: Nicholas
authors: N
authors: Wareham
authors: John
authors: J
authors: Reilly
authors: Chris
authors: C
authors: Riddoch
mesh_terms: D002648:Child; D003625:Data Collection / Q000295:instrumentation*; D015444:Exercise; D006801:Humans; D018670:Monitoring, Ambulatory / Q000295:instrumentation; D015203:Reproducibility of Results; D012959:Socioeconomic Factors