title: The validation of Fibit Zip™ physical activity monitor as a measure of free-living physical activity.
abstract: BACKGROUND
  The new generation of activity monitors allow users to upload their data to the internet and review progress. The aim of this study is to validate the Fitbit Zip as a measure of free-living physical activity.
  
  
  RESULTS
  Participants wore a Fitbit Zip, ActiGraph GT3X accelerometer and a Yamax CW700 pedometer for seven days. Participants were asked their opinion on the utility of the Fitbit Zip. Validity was assessed by comparing the output using Spearman's rank correlation coefficients, Wilcoxon signed rank tests and Bland-Altman plots. 59.5% (25/47) of the cohort were female. There was a high correlation in steps/day between the Fitbit Zip and the two reference devices (r = 0.91, p < 0.001). No statistically significant difference between the Fitbit and Yamax steps/day was observed (Median (IQR) 7477 (3597) vs 6774 (3851); p = 0.11). The Fitbit measured significantly more steps/day than the Actigraph (7477 (3597) vs 6774 (3851); p < 0.001). Bland-Altman plots revealed no systematic differences between the devices.
  
  
  CONCLUSIONS
  Given the high level of correlation and no apparent systematic biases in the Bland Altman plots, the use of Fitbit Zip as a measure of physical activity. However the Fitbit Zip recorded a significantly higher number of steps per day than the Actigraph.
authors.affiliation: Centre for Public Health, School of Medicine, Dentistry and Biomedical Sciences, Queens' University Belfast, Belfast, UK. m.tully@qub.ac.uk.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tully
authors.forename: Cairmeal
authors.initials: C
authors.lastname: McBride
authors.forename: Leonnie
authors.initials: L
authors.lastname: Heron
authors.forename: Ruth F
authors.initials: RF
authors.lastname: Hunter
mesh_terms: D061725:Accelerometry / Q000295:instrumentation; D056044:Actigraphy / Q000295:instrumentation; D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D057187:Independent Living / Q000706:statistics & numerical data*; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D010809:Physical Fitness; D015203:Reproducibility of Results; D013686:Telemetry / Q000295:instrumentation*; D016138:Walking; D055815:Young Adult