Assessing the Measurement Properties of the Fitbit Zip® Among Adults Living With HIV

in Journal of Physical Activity and Health
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Purpose: To assess the criterion and construct validity of the Fitbit Zip® to measure physical activity among adults living with HIV. Methods: Participants were video recorded completing 2 walk tests while wearing the Fitbit Zip® and completed 3 self-reported physical activity questionnaires 1 week later. The authors calculated intraclass correlation coefficients (ICCs) to determine agreement between the number of steps taken and distance walked (Fitbit Zip®) with the visual count of number of steps taken and actual distance walked (walk tests). The authors tested 15 a priori hypotheses about predicted associations between questionnaire scores and physical activity measured by the Fitbit Zip®. Results: Among the 34 participants, there was “excellent” agreement between the number of steps taken measured by the Fitbit Zip® and visually counted number of steps taken (ICC = .99) and number of steps taken at slow (ICC = .75), moderate (ICC = .85), and fast (ICC = .78) walking speeds. There was “poor” agreement between the Fitbit Zip® recorded distance and actual determined distance walked (ICC = .20). Three (20%) construct validity hypotheses were confirmed. Conclusions: The Fitbit Zip® demonstrated criterion validity for its ability to measure number of steps taken but not distance walked, and did not demonstrate construct validity for measuring physical activity among adults with HIV.

Dagenais, Salbach, Brooks, and O’Brien are with Rehabilitation Sciences Institute (RSI), University of Toronto, Toronto, ON, Canada. Salbach and O’Brien are also with the Department of Physical Therapy, University of Toronto, Toronto, ON, Canada. Brooks is also with the School of Rehabilitation Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada. O’Brien is also with the Institute of Health Policy, Management and Evaluation (IHPME), University of Toronto, Toronto, ON, Canada.

O’Brien (kelly.obrien@utoronto.ca) is corresponding author.
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