title: Effects of Varying Epoch Lengths, Wear Time Algorithms, and Activity Cut-Points on Estimates of Child Sedentary Behavior and Physical Activity from Accelerometer Data.
abstract: OBJECTIVE
  To examine the effects of accelerometer epoch lengths, wear time (WT) algorithms, and activity cut-points on estimates of WT, sedentary behavior (SB), and physical activity (PA).
  
  
  METHODS
  268 7-11 year-olds with BMI ≥ 85th percentile for age and sex wore accelerometers on their right hips for 4-7 days. Data were processed and analyzed at epoch lengths of 1-, 5-, 10-, 15-, 30-, and 60-seconds. For each epoch length, WT minutes/day was determined using three common WT algorithms, and minutes/day and percent time spent in SB, light (LPA), moderate (MPA), and vigorous (VPA) PA were determined using five common activity cut-points. ANOVA tested differences in WT, SB, LPA, MPA, VPA, and MVPA when using the different epoch lengths, WT algorithms, and activity cut-points.
  
  
  RESULTS
  WT minutes/day varied significantly by epoch length when using the NHANES WT algorithm (p < .0001), but did not vary significantly by epoch length when using the ≥ 20 minute consecutive zero or Choi WT algorithms. Minutes/day and percent time spent in SB, LPA, MPA, VPA, and MVPA varied significantly by epoch length for all sets of activity cut-points tested with all three WT algorithms (all p < .0001). Across all epoch lengths, minutes/day and percent time spent in SB, LPA, MPA, VPA, and MVPA also varied significantly across all sets of activity cut-points with all three WT algorithms (all p < .0001).
  
  
  CONCLUSIONS
  The common practice of converting WT algorithms and activity cut-point definitions to match different epoch lengths may introduce significant errors. Estimates of SB and PA from studies that process and analyze data using different epoch lengths, WT algorithms, and/or activity cut-points are not comparable, potentially leading to very different results, interpretations, and conclusions, misleading research and public policy.
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Stanford Prevention Research Center, Department of Medicine, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Banda
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Division of General Pediatrics, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: K Farish
authors.initials: KF
authors.lastname: Haydel
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Division of General Pediatrics, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Tania
authors.initials: T
authors.lastname: Davila
authors.affiliation: Quantitative Sciences Unit, Department of Medicine, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Manisha
authors.initials: M
authors.lastname: Desai
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Division of General Pediatrics, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Susan
authors.initials: S
authors.lastname: Bryson
authors.affiliation: Stanford Prevention Research Center, Department of Medicine, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: William L
authors.initials: WL
authors.lastname: Haskell
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Division of General Pediatrics, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Donna
authors.initials: D
authors.lastname: Matheson
authors.affiliation: Stanford Solutions Science Lab, Department of Pediatrics and Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, California, United States of America.|Stanford Prevention Research Center, Department of Medicine, Stanford University School of Medicine, Stanford, California, United States of America.|Division of General Pediatrics, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Robinson
mesh_terms: D061725:Accelerometry / Q000706:statistics & numerical data*; D000293:Adolescent; D000465:Algorithms; D000704:Analysis of Variance; D015992:Body Mass Index; D002648:Child; D002652:Child Behavior / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D011640:Public Policy; D057185:Sedentary Behavior; D013997:Time Factors