title: Objective measurement of sedentary behavior: impact of non-wear time rules on changes in sedentary time.
abstract: BACKGROUND
  Accelerometry non-wear time rules might affect sedentary time, and the associations with health outcomes such as adiposity. However, the exact effect of different non-wear time rules on sedentary time and reported changes in sedentary time is unknown. This study evaluated the effect of different accelerometry non-wear time rules on sedentary time and changes in sedentary time from age 9-12 years.
  
  
  METHODS
  Accelerometry data were collected as part of the Gateshead Millennium Birth Cohort study. Participants were 9.3 (± 0.4) years at baseline (n =  17) and 12.5 (± 0.3) years at follow-up (n = 440). Sedentary time was defined using an accelerometry cut-point of 25 counts per 15 s. Non-wear time was defined using manual data reduction (the reference method) and 10 min, 20 min and 60 min consecutive zeros. Differences between methods were analyzed using repeated measures ANOVA with Bonferroni post-hoc analyses.
  
  
  RESULTS
  Mean daily sedentary time at age 9 ranged from 364 min per day to 426 min using the 10 min and 60 min rule, respectively (p < 0.05). At 12 years, mean daily sedentary times ranged from 424 min to 518 min (p < 0.05). Mean changes in daily sedentary time over the three years ranged from 60 min to 93 min using the 10 min and 60 min rule, respectively (p < 0.05). When adjusting for wear time, differences in average sedentary time between methods decreased from 62 min to 27 min (age 9), 95 min to 32 min (age 12) and 33 min to 10 min (changes between 9 to 12 years).
  
  
  CONCLUSIONS
  Using different non-wear time rules results in significant differences in daily sedentary time and changes in sedentary time. Correcting for wear time appears to be a reasonable approach to limiting these differences and may improve comparability between future studies. Using the 20 min rule, while correcting for wear time, provided the most accurate estimates of sedentary time and changes in sedentary time, compared to the manual reference in 9-12 year-olds.
authors.affiliation: School of Psychological Sciences and Health, University of Strathclyde, Glasgow, Scotland, G1 1QN, UK. xanne.janssen@strath.ac.uk.
authors.forename: Xanne
authors.initials: X
authors.lastname: Janssen
authors.affiliation: Institute of Health & Society, Human Nutrition Research Centre, Newcastle University, Newcastle Upon Tyne, UK. laura.basterfield@newcastle.ac.uk.
authors.forename: Laura
authors.initials: L
authors.lastname: Basterfield
authors.affiliation: Institute of Health & Society, Human Nutrition Research Centre, Newcastle University, Newcastle Upon Tyne, UK. kathryn.parkinson@newcastle.ac.uk.
authors.forename: Kathryn N
authors.initials: KN
authors.lastname: Parkinson
authors.affiliation: Institute of Health & Society Newcastle, Sir James Spence Institute of Child Health, Royal Victoria Infirmary, Newcastle University, Newcastle Upon Tyne, UK. mark.pearce@newcastle.ac.uk.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Pearce
authors.affiliation: Institute of Health & Society, Human Nutrition Research Centre, Newcastle University, Newcastle Upon Tyne, UK. jessica.reilly@newcastle.ac.uk.
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Reilly
authors.affiliation: Institute of Health & Society, Human Nutrition Research Centre, Newcastle University, Newcastle Upon Tyne, UK. ashley.adamson@newcastle.ac.uk.
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Adamson
authors.affiliation: School of Psychological Sciences and Health, University of Strathclyde, Glasgow, Scotland, G1 1QN, UK. john.j.reilly@strath.ac.uk.
authors.forename: John J
authors.initials: JJ
authors.lastname: Reilly
mesh_terms: D061725:Accelerometry / Q000379:methods*; D050154:Adiposity; D002648:Child; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D057185:Sedentary Behavior; D013997:Time Factors