title: Quality control and data reduction procedures for accelerometry-derived measures of physical activity.
abstract: BACKGROUND
  This article describes four key quality control and data reduction issues that researchers should consider when using accelerometry to measure physical activity: monitor reliability, spurious data, monitor wear time, and number of valid days required for analysis.
  
  
  METHODS
  Exploratory analyses were conducted on an unweighted subsample (n=987) of the accelerometry data from the Canadian Health Measures Survey. Participants were asked to wear an accelerometer for 7 consecutive days. Calibration, reliability, biological plausibility and compliance issues were explored using descriptive statistics.
  
  
  RESULTS
  Ongoing calibration is an effective method for identifying malfunctioning accelerometers. The percentage of files deemed viable for analysis depends on participant compliance, the allowable interruption period chosen and the minimum wear-time-per-day criterion. A 60-minute allowable interruption period and 10-hours-per-day wear time criteria resulted in 95% of the subsample having at least 1 valid day, and 84% having at least 4 valid days.
  
  
  CONCLUSIONS
  Before the derivation of physical activity outcomes, accelerometry data should undergo standardized quality control and data reduction procedures to prevent mis-representation of the results. Incomplete accelerometry data should be handled carefully, and strategies to improve compliance in the field are warranted.
authors.affiliation: Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario. Rachel.Colley@statcan.gc.ca
authors.forename: Rachel
authors.initials: R
authors.lastname: Colley
authors.forename: Sarah
authors.initials: S
authors.lastname: Connor Gorber
authors.forename: Mark S
authors.initials: MS
authors.lastname: Tremblay
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D005080:Exercise Test / Q000295:instrumentation; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000295:instrumentation* / Q000592:standards*; D009043:Motor Activity / Q000502:physiology*; D011786:Quality Control; D015203:Reproducibility of Results; D012107:Research Design / Q000592:standards*; D013997:Time Factors; D016138:Walking; D055815:Young Adult