title: Performance of the ActiGraph accelerometer using a national population-based sample of youth and adults.
abstract: BACKGROUND
  Accelerometer output may be semi-continuous or continuous in nature, which has implications on discerning non-wear and defining physical activity intensity levels. This study described field-based accelerometer performance from a surveillance sample of youth and adults.
  
  
  METHODS
  Using 2003-2006 National Health and Nutrition Examination Survey data, 4,028 youth ages 6 to 17 years and 7,931 adults age > =18 years wore an ActiGraph AM7164 accelerometer for one week, providing at least 3 days of wear for > =8 hours/day. Accelerometer performance was assessed by exploring the number of different values of accelerometer counts/minute for each participant.
  
  
  RESULTS
  On average, youth participants had 1381 different counts/minute over 7 days (median 1360, interquartile range 1127-1623) and adult participants had 1101 different counts/minute over 7 days (median 1085, interquartile range 874-1313). For both youth and adults, when restricting to counts/minute between 0 to 4999, every possible value (in counts/minute) occurred at least once.
  
  
  CONCLUSIONS
  The field-based data confirmed that the accelerometer used in this study allowed for continuous counts/minute through which all but the most vigorous activities would usually occur.
authors.affiliation: Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina, 137 East Franklin Street, Suite 306, Chapel Hill, North Carolina, 27514, USA. Kelly_evenson@unc.edu.
authors.forename: Kelly R
authors.initials: KR
authors.lastname: Evenson
authors.affiliation: Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina, 137 East Franklin Street, Suite 306, Chapel Hill, North Carolina, 27514, USA. Molly_wen@unc.edu.
authors.forename: Fang
authors.initials: F
authors.lastname: Wen
mesh_terms: D061725:Accelerometry / Q000295:instrumentation*; D056044:Actigraphy / Q000295:instrumentation*; D000293:Adolescent; D000328:Adult; D002648:Child; D003710:Demography; D006262:Health; D006801:Humans; D009749:Nutrition Surveys; D055815:Young Adult