Wear Time Validation Defaults
The defaults defined for Wear Time screening (60 minutes of consecutive zeros with a 2 minute spike tolerance) were loosely derived from the research note Identification of accelereometer non-wear time and sedentary behavior in the Research Quartely for Exercise and Sport, submitted to the journal on June 1, 2010. Permission to share this article publically has been requested by ActiGraph to the managing editor of Research Quarterly for Exercise and Sport.
Cut Point Defaults
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"Default" set - Cut points for counts greater than 1952 were derived from research performed by Freedson, Melanson, and Sirard in Calibration of the Computer Science and Applications, Inc. Accelerometer. Cut points for the "Light" range were defined by the research performed by Charles Matthews entitled Calibration of Accelerometer Output for Adults.
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"Vector Magnitude (VM3)" set - Cut points for the VM3 vector magnitude defaults were derived from the Journal of Science and Medicine in Sport article entitled Validation and Comparison of ActiGraph Activity Monitors (in-press) by J. Sasaki, D. John, and P. Freedson.
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Children's set - Children's cut points default values were derived from work performed by P. Freedson, D. Pober, and K. Janz entitled Calibration of Accelerometer Output for Children (page 3 of the full article)
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Preschool set - Preschooler cut points were dereived from fundamental research performed by R. Pate, M. Almeida, K. McIver, K. Pfeiffer, and M. Dowda in Validation and Calibration of an Accelerometer in Preschool Children.
Bout Detection Defaults
METS
Two algorithms are used for the MET rate calculations in ActiLife.
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The Adult METs formula is used for subjects 18 years and older. The standard formula for Metabolic Equivalent is used. Specifically, one MET is defined as 1 kcal/(kg/hour) where kcal is the kcal equivalent as computed from our device counts using the Freedson Equation defined in Calibration of the Computer Science and Applications, Inc. Accelerometer and kg is the subject's weight in kilograms (automatically calculated if lbs are used). METs are calculated on a per-epoch basis (60 second epochs are required for this tool) and are averaged to obtain hourly MET levels.
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The MET formula used for children is METs = 2.757 + (0.0015 x counts per minute) - (0.08957 x age(yr)) - (0.000038 x counts per minute x age(yr). This formula was taken from Predicitive Validity of Three ActiGraph Energy Expenditure Equations for Children by S. Trost, R. Way, and A. Okely.