title: Comparison of GT3X accelerometer and YAMAX pedometer steps/day in a free-living sample of overweight and obese adults.
abstract: BACKGROUND
  The purpose of this study was to compare steps/day detected by the YAMAX SW-200 pedometer versus the Actigraph GT3X accelerometer in free-living adults.
  
  
  METHODS
  Daily YAMAX and GT3X steps were collected from a sample of 23 overweight and obese participants (78% female; age = 52.6 ± 8.4 yr.; BMI = 31.0 ± 3.7 m·kg-2). Because a pedometer is more likely to be used in a community-based intervention program, it was used as the standard for comparison. Percent difference (PD) and absolute percent difference (APD) were calculated to examine between-instrument agreement. In addition, days were categorized based on PD: a) under-counting (> -10 PD), b) acceptable counting (-10 to 10 PD), and c) over-counting (> 10 PD).
  
  
  RESULTS
  The YAMAX and GT3X detected 8,025 ± 3,967 and 7131 ± 3066 steps/day, respectively, and the outputs were highly correlated (r = .87). Average PD was -3.1% ± 30.7% and average APD was 23.9% ± 19.4%. Relative to the YAMAX, 53% of the days detected by the GT3X were classified as under-counting, 25% acceptable counting, and 23% over-counting.
  
  
  CONCLUSIONS
  Although the output of these 2 instruments is highly correlated, caution is advised when directly comparing or using their output interchangeably.
authors: Dept of Population Science, Pennington Biomedical Research Center, Baton Rouge, LA, USA.
authors: Tiago V
authors: TV
authors: Barriera
authors: Catrine
authors: C
authors: Tudor-Locke
authors: Catherine M
authors: CM
authors: Champagne
authors: Stephanie T
authors: ST
authors: Broyles
authors: William D
authors: WD
authors: Johnson
authors: Peter T
authors: PT
authors: Katzmarzyk
mesh_terms: D061725:Accelerometry; D000328:Adult; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009765:Obesity / Q000628:therapy; D050177:Overweight / Q000628:therapy*; D015203:Reproducibility of Results; D016138:Walking