title: The effect of reintegrating Actigraph accelerometer counts in preschool children: comparison using different epoch lengths.
abstract: OBJECTIVE
  The purpose of this study was to determine whether ActiGraph accelerometer activity counts and estimates of moderate-to-vigorous physical activity collected at a single larger epoch are comparable to those collected at smaller epochs reintegrated into a larger epoch.
  
  
  METHODS
  A cross-sectional study design.
  
  
  METHODS
  Thirty-one preschoolers (3-5years) concurrently wore four accelerometers that were each initialized at four different epoch lengths (1s, 15s, 30s, and 60s) during a full preschool day. Counts collected at 1s, 15s, and 30s epoch were each reintegrated and compared to those collected at a larger epoch (e.g., counts from one 15s epoch vs. consecutive sum of counts from fifteen 1s epochs). Six sets of cut-points (Pate, Freedson, Sirard, Van Cauwenberghe, Evenson and Puyau) were applied to estimate moderate-to-vigorous physical activity minutes. Paired t-test and Cohen's d were used to compare group mean differences. Absolute percent errors Bland-Altman plots with limits of agreement were used to compare individual differences.
  
  
  RESULTS
  Minimal group mean differences were found for counts and moderate-to-vigorous physical activity estimates between larger and reintegrated epochs. Relatively smaller absolute percent errors (6.2-9.2%) and limits of agreements (-15.52%, 18.00% to -28.27%, 28.02%) were observed for counts than absolute percent errors (10.1-50.3%) and limits of agreements (-27.3%, 33.3% to -156.9%, 137.9%) for moderate-to-vigorous physical activity estimates.
  
  
  CONCLUSIONS
  Smaller individual differences in activity counts tended to yield larger individual variations in moderate-to-vigorous physical activity estimates, despite minimal group mean differences. Therefore, researchers reintegrating smaller epochs into a larger epoch should be conscious of possible differences in moderate-to-vigorous physical activity estimates obtained from a single larger epoch.
authors: Department of Exercise Science, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA. myungshingo@gmail.com
authors: Youngwon
authors: Y
authors: Kim
authors: Michael W
authors: MW
authors: Beets
authors: Russell R
authors: RR
authors: Pate
authors: Steven N
authors: SN
authors: Blair
mesh_terms: D056044:Actigraphy / Q000295:instrumentation / Q000379:methods*; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D015203:Reproducibility of Results; D013997:Time Factors