title: Whole-day and segmented-day physical activity variability of northwest England school children.
abstract: OBJECTIVE
  This study aimed to (1) assess the day-to-day variability of children's weekday physical activity for the whole-day, and when segmented into discrete periods of the day; and (2) compare boys' and girls' physical activity variability.
  
  
  METHODS
  Fifty-eight children (aged 7-11 years; 31 boys) from a northwest England city wore accelerometers for 4 consecutive weekdays during November and December 2005. Intra-class correlations (ICCs) were calculated for 1 and 4 monitored days and segments of days to determine reliable estimates of moderate-to-vigorous physical activity (MVPA). The Spearman-Brown prophecy formula established the number of monitoring days required for 80% reliability.
  
  
  RESULTS
  Higher ICC coefficients were typically observed among boys. Eight days of boys' whole-day monitoring were needed to achieve a reliability of 0.8, while 10 days were required for girls. The pre-school segment was the most stable (boys' ICC=0.862; girls' ICC=0.770). Compared to girls, fewer days of boys' monitoring would be required during all segments other than the school day.
  
  
  CONCLUSIONS
  Day-to-day physical activity variability was sex-specific, with boys' MVPA generally more stable than girls'. The greatest reliability occurred between 7 am and 3 pm, suggesting that physical activity behaviors are more consistent in the school environment.
authors.affiliation: REACH Group, Liverpool John Moores University, UK. s.j.fairclough@ljmu.ac.uk
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Fairclough
authors.forename: Zoe H
authors.initials: ZH
authors.lastname: Butcher
authors.forename: Gareth
authors.initials: G
authors.lastname: Stratton
mesh_terms: D002648:Child; D003430:Cross-Sectional Studies; D004739:England; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D016138:Walking