title: Measurement effects of seasonal and monthly variability on pedometer-determined data.
abstract: BACKGROUND
  The seasonal and monthly variability of pedometer-determined physical activity and its effects on accurate measurement have not been examined. The purpose of the study was to reduce measurement error in step-count data by controlling a) the length of the measurement period and b) the season or month of the year in which sampling was conducted.
  
  
  METHODS
  Twenty-three middle-aged adults were instructed to wear a Yamax SW-200 pedometer over 365 consecutive days. The step-count measurement periods of various lengths (eg, 2, 3, 4, 5, 6, 7 days, etc.) were randomly selected 10 times for each season and month. To determine accurate estimates of yearly step-count measurement, mean absolute percentage error (MAPE) and bias were calculated. The year-round average was considered as a criterion measure. A smaller MAPE and bias represent a better estimate.
  
  
  RESULTS
  Differences in MAPE and bias among seasons were trivial; however, they varied among different months. The months in which seasonal changes occur presented the highest MAPE and bias.
  
  
  CONCLUSIONS
  Targeting the data collection during certain months (eg, May) may reduce pedometer measurement error and provide more accurate estimates of year-round averages.
authors.affiliation: Dept of Health and Human Performance, Middle Tennessee State University, Murfreesboro, TN, USA.
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kang
authors.forename: David R
authors.initials: DR
authors.lastname: Bassett
authors.forename: Tiago V
authors.initials: TV
authors.lastname: Barreira
authors.forename: Catrine
authors.initials: C
authors.lastname: Tudor-Locke
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Ainsworth
mesh_terms: D000328:Adult; D015982:Bias; D003625:Data Collection / Q000379:methods; D005260:Female; D015438:Health Behavior; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000379:methods; D009043:Motor Activity / Q000502:physiology*; D015203:Reproducibility of Results; D012621:Seasons; D013997:Time Factors; D016138:Walking / Q000502:physiology*