title: Reliability and validity of ten consumer activity trackers.
abstract: BACKGROUND
  Activity trackers can potentially stimulate users to increase their physical activity behavior. The aim of this study was to examine the reliability and validity of ten consumer activity trackers for measuring step count in both laboratory and free-living conditions.
  
  
  METHODS
  Healthy adult volunteers (n = 33) walked twice on a treadmill (4.8 km/h) for 30 min while wearing ten different activity trackers (i.e. Lumoback, Fitbit Flex, Jawbone Up, Nike+ Fuelband SE, Misfit Shine, Withings Pulse, Fitbit Zip, Omron HJ-203, Yamax Digiwalker SW-200 and Moves mobile application). In free-living conditions, 56 volunteers wore the same activity trackers for one working day. Test-retest reliability was analyzed with the Intraclass Correlation Coefficient (ICC). Validity was evaluated by comparing each tracker with the gold standard (Optogait system for laboratory and ActivPAL for free-living conditions), using paired samples t-tests, mean absolute percentage errors, correlations and Bland-Altman plots.
  
  
  RESULTS
  Test-retest analysis revealed high reliability for most trackers except for the Omron (ICC .14), Moves app (ICC .37) and Nike+ Fuelband (ICC .53). The mean absolute percentage errors of the trackers in laboratory and free-living conditions respectively, were: Lumoback (-0.2, -0.4), Fibit Flex (-5.7, 3.7), Jawbone Up (-1.0, 1.4), Nike+ Fuelband (-18, -24), Misfit Shine (0.2, 1.1), Withings Pulse (-0.5, -7.9), Fitbit Zip (-0.3, 1.2), Omron (2.5, -0.4), Digiwalker (-1.2, -5.9), and Moves app (9.6, -37.6). Bland-Altman plots demonstrated that the limits of agreement varied from 46 steps (Fitbit Zip) to 2422 steps (Nike+ Fuelband) in the laboratory condition, and 866 steps (Fitbit Zip) to 5150 steps (Moves app) in the free-living condition.
  
  
  CONCLUSIONS
  The reliability and validity of most trackers for measuring step count is good. The Fitbit Zip is the most valid whereas the reliability and validity of the Nike+ Fuelband is low.
authors.affiliation: Research group Healthy ageing, Allied health care and Nursing, Hanze University of Applied Sciences, Groningen, The Netherlands.
authors.forename: Thea J M
authors.initials: TJ
authors.lastname: Kooiman
authors.affiliation: CBO Groningen: Center for Physical Activity and Research, Groningen, The Netherlands ; Quantified Self Institute, Hanze University of Applied Sciences, Groningen, The Netherlands.
authors.forename: Manon L
authors.initials: ML
authors.lastname: Dontje
authors.affiliation: CBO Groningen: Center for Physical Activity and Research, Groningen, The Netherlands.
authors.forename: Siska R
authors.initials: SR
authors.lastname: Sprenger
authors.affiliation: Research group Healthy ageing, Allied health care and Nursing, Hanze University of Applied Sciences, Groningen, The Netherlands.
authors.forename: Wim P
authors.initials: WP
authors.lastname: Krijnen
authors.affiliation: Research group Healthy ageing, Allied health care and Nursing, Hanze University of Applied Sciences, Groningen, The Netherlands.
authors.forename: Cees P
authors.initials: CP
authors.lastname: van der Schans
authors.affiliation: Research group Healthy ageing, Allied health care and Nursing, Hanze University of Applied Sciences, Groningen, The Netherlands ; Quantified Self Institute, Hanze University of Applied Sciences, Groningen, The Netherlands.
authors.forename: Martijn
authors.initials: M
authors.lastname: de Groot
keywords: Accelerometry; Activity trackers; Free-living; Reliability; Validation study