title: Impact of methodological decisions on accelerometer outcome variables in young children.
abstract: BACKGROUND
  The impact of accelerometer-related methodological decisions relating to the assessment of physical activity and sedentary time has not been conclusively determined in young children.
  
  
  OBJECTIVE
  To determine the effects of epoch and cutoff points on the assessment of physical activity and sedentary time and to determine the accelerometer wear time required to achieve reliable accelerometer data in children.
  
  
  METHODS
  Children were recruited from centres at Ghent, Glasgow, Gothenburg and Zaragoza.
  
  
  METHODS
  Physical activity was assessed for 1 week in 86 children (41 girls, 45 boys; mean age 7±2 years) by uniaxial accelerometry. The epoch was set at 15 s and reintegrated to 30 and 60 s. Time spent sedentary and in moderate and vigorous physical activity (MVPA) was assessed using a range of cutoff points. Number of days required to achieve 80% reliability was predicted using the Spearman-Brown Prophecy formula.
  
  
  RESULTS
  The Reilly cutoff points (<1100 counts per min (CPM)) indicated less sedentary time per day when comparing 15 vs 30 s and 15 vs 60 s epochs: 570±91 vs 579±93 min and 570±91 vs 579±94 min, respectively; P<0.05. Pate cutoff points (>420 counts per 15 s) reported more MVPA time per day compared with Sirard (890 counts per 15 s) and Puyau cutoff points (>3200 counts per min) using 15 s epoch: 78 (4-197) min (median (range) vs 18 (1-80) min and 24 (1-100) min, respectively; P<0.001. Compliance with guidelines of at least 60 min MVPA was 84, 78 and 73% for Pate cutoff points using 15, 30 and 60 s epochs, respectively, but 0% for Sirard and Puyau cutoff points across epochs. The number of days required to achieve 80% reliability for CPM, sedentary and MVPA time was 7.4-8.5 days.
  
  
  CONCLUSIONS
  Choice of epoch and cutoff point significantly influenced the classification of sedentary and MVPA time and observed compliance to the MVPA guidelines.
authors.affiliation: College of Medicine, Veterinary and Life Sciences, University of Glasgow, UK.
authors.forename: R
authors.initials: R
authors.lastname: Ojiambo
authors.forename: R
authors.initials: R
authors.lastname: Cuthill
authors.forename: H
authors.initials: H
authors.lastname: Budd
authors.forename: K
authors.initials: K
authors.lastname: Konstabel
authors.forename: J A
authors.initials: JA
authors.lastname: Casajús
authors.forename: A
authors.initials: A
authors.lastname: González-Agüero
authors.forename: E
authors.initials: E
authors.lastname: Anjila
authors.forename: J J
authors.initials: JJ
authors.lastname: Reilly
authors.forename: C
authors.initials: C
authors.lastname: Easton
authors.forename: Y P
authors.initials: YP
authors.lastname: Pitsiladis
mesh_terms: D000054:Acceleration; D002648:Child; D003657:Decision Making; D015444:Exercise; D005080:Exercise Test / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation / Q000379:methods*; D009043:Motor Activity / Q000502:physiology*; D057185:Sedentary Behavior