title: Actigraph-defined moderate-to-vigorous physical activity cut-off points among children: statistical and biobehavioural relevance.
abstract: OBJECTIVE
  To compare Actigraph-defined moderate-to-vigorous physical activity (MVPA) cutpoints among children, combining statistical and biobehavioural analyses.
  
  
  METHODS
  One hundred and thirteen children aged 10.0 +/- 0.8 years wore accelerometer for three days. The time they spent in MVPA was estimated using 10 thresholds ranged from 3000 to 3900 cpm. A statistical construct including 45 Bland and Altman pairwise analyses was used to compare the 10 estimates of MVPA. A regression was performed to develop an equation relating mean differences to the between-cutpoint gaps.
  
  
  RESULTS
  Mean differences in the MVPA estimates ranged from 1.6 to 12.8 min as a function of increment. Raw estimates of MVPA decreased according to an arithmetic sequence with a common difference of 200 cpm. This difference translates into a drop of 12% in MVPA and a misclassification of up to 5% of children. Mean differences (Y) could be predicted from increments (X) using: Y= 0.02 X (R(2)= 0.99, SEE = 0.72, p < 0.0001).
  
  
  CONCLUSIONS
  When a lack of agreement should be assumed as the between-cutpoint gap exceeds 200 cpm, statistical differences may occur earlier at 90 cpm. Yet, the current equation makes it possible to compare and adjust results from studies/interventions using diverse cutpoints for MVPA among children.
authors.affiliation: Institute of Engineering in Health of Lille, EA 2694: Laboratory of Public Health, University of Lille 2, France. ben.guinhouya@gmail.com
authors.forename: Comlavi B
authors.initials: CB
authors.lastname: Guinhouya
authors.forename: Mohamed
authors.initials: M
authors.lastname: Lemdani
authors.forename: Christian
authors.initials: C
authors.lastname: Vilhelm
authors.forename: Alain
authors.initials: A
authors.lastname: Durocher
authors.forename: Hervé
authors.initials: H
authors.lastname: Hubert
mesh_terms: D015982:Bias; D001827:Body Height; D015992:Body Mass Index; D002648:Child; D016552:Ergometry / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods; D009043:Motor Activity / Q000502:physiology*; D019370:Observation; D005082:Physical Exertion / Q000502:physiology*; D015203:Reproducibility of Results