title: Accelerometer wear-site detection: When one site does not suit all, all of the time.
abstract: OBJECTIVE
  Choice of accelerometer wear-site may facilitate greater compliance in research studies. We aimed to test whether a simple method could automatically discriminate whether an accelerometer was worn on the hip or wrist from free-living data.
  
  
  METHODS
  Cross-sectional.
  
  
  METHODS
  Twenty-two 10-12y old children wore a GENEActiv at the wrist and at the hip for 7-days. The angle between the forearm and the total acceleration vector for the wrist-worn monitor and between the pelvis and the total acceleration vector for the hip-worn monitor (i.e. the angle between the Y-axis component of the acceleration and the total acceleration vector) was calculated for each 5s epoch. The standard deviation of this angle (SDangle) was calculated over time for the wrist-worn and hip-worn monitor for windows of varying lengths. We hypothesised that the wrist angle would be more variable than the hip angle.
  
  
  RESULTS
  Wear site could be discriminated based on SDangle; the shorter the time window the lower the optimal threshold and Area under the Receiver-Operating-Characteristic curve (AUROC) for discrimination of wear-site (AUROC=0.833 (1min) - 0.952 (12h)). Classification accuracy was good for windows of 8min (sensitivity=90%, specificity=87%, AUROC=0.92) and plateaued for windows of ≥60min (sensitivity and specificity >90%, AUROC=0.95-0.96).
  
  
  CONCLUSIONS
  We have presented a robust, computationally simple method that detects whether an accelerometer is being worn on the hip or wrist from 8 to 60min of data. This facilitates the use of wear-site specific algorithms to analyse accelerometer data.
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester Diabetes Centre, Leicester General Hospital, United Kingdom; National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Leicester Diabetes Centre, Leicester General Hospital, United Kingdom; Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Australia. Electronic address: alex.rowlands@le.ac.uk.
authors.forename: Alex V
authors.initials: AV
authors.lastname: Rowlands
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Australia.
authors.forename: Tim S
authors.initials: TS
authors.lastname: Olds
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester Diabetes Centre, Leicester General Hospital, United Kingdom; National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Leicester Diabetes Centre, Leicester General Hospital, United Kingdom.
authors.forename: Kishan
authors.initials: K
authors.lastname: Bakrania
authors.affiliation: Early Start Research Institute, University of Wollongong, Australia.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Stanley
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Australia.
authors.forename: Gaynor
authors.initials: G
authors.lastname: Parfitt
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Australia.
authors.forename: Roger G
authors.initials: RG
authors.lastname: Eston
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester Diabetes Centre, Leicester General Hospital, United Kingdom; National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Leicester Diabetes Centre, Leicester General Hospital, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Yates
authors.affiliation: Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Australia.
authors.forename: François
authors.initials: F
authors.lastname: Fraysse
mesh_terms: D061725:Accelerometry / Q000379:methods*; D000465:Algorithms; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006615:Hip; D006801:Humans; D008297:Male; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014953:Wrist
keywords: Activity monitor; GENEActiv; Hip; Wrist