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Accuracy of Fitbit Devices: Systematic Review and Narrative Syntheses of Quantitative Data - PubMed

  • ️Mon Jan 01 2018

Review

. 2018 Aug 9;6(8):e10527.

doi: 10.2196/10527.

Affiliations

Review

Accuracy of Fitbit Devices: Systematic Review and Narrative Syntheses of Quantitative Data

Lynne M Feehan et al. JMIR Mhealth Uhealth. 2018.

Abstract

Background: Although designed as a consumer product to help motivate individuals to be physically active, Fitbit activity trackers are becoming increasingly popular as measurement tools in physical activity and health promotion research and are also commonly used to inform health care decisions.

Objective: The objective of this review was to systematically evaluate and report measurement accuracy for Fitbit activity trackers in controlled and free-living settings.

Methods: We conducted electronic searches using PubMed, EMBASE, CINAHL, and SPORTDiscus databases with a supplementary Google Scholar search. We considered original research published in English comparing Fitbit versus a reference- or research-standard criterion in healthy adults and those living with any health condition or disability. We assessed risk of bias using a modification of the Consensus-Based Standards for the Selection of Health Status Measurement Instruments. We explored measurement accuracy for steps, energy expenditure, sleep, time in activity, and distance using group percentage differences as the common rubric for error comparisons. We conducted descriptive analyses for frequency of accuracy comparisons within a ±3% error in controlled and ±10% error in free-living settings and assessed for potential bias of over- or underestimation. We secondarily explored how variations in body placement, ambulation speed, or type of activity influenced accuracy.

Results: We included 67 studies. Consistent evidence indicated that Fitbit devices were likely to meet acceptable accuracy for step count approximately half the time, with a tendency to underestimate steps in controlled testing and overestimate steps in free-living settings. Findings also suggested a greater tendency to provide accurate measures for steps during normal or self-paced walking with torso placement, during jogging with wrist placement, and during slow or very slow walking with ankle placement in adults with no mobility limitations. Consistent evidence indicated that Fitbit devices were unlikely to provide accurate measures for energy expenditure in any testing condition. Evidence from a few studies also suggested that, compared with research-grade accelerometers, Fitbit devices may provide similar measures for time in bed and time sleeping, while likely markedly overestimating time spent in higher-intensity activities and underestimating distance during faster-paced ambulation. However, further accuracy studies are warranted. Our point estimations for mean or median percentage error gave equal weighting to all accuracy comparisons, possibly misrepresenting the true point estimate for measurement bias for some of the testing conditions we examined.

Conclusions: Other than for measures of steps in adults with no limitations in mobility, discretion should be used when considering the use of Fitbit devices as an outcome measurement tool in research or to inform health care decisions, as there are seemingly a limited number of situations where the device is likely to provide accurate measurement.

Keywords: Fitbit; accuracy; data accuracy; distance; energy expenditure; energy metabolism; fitness trackers; review; sleep; steps; systematic review; time in activity; wearable activity tracker.

©Lynne M Feehan, Jasmina Geldman, Eric C Sayre, Chance Park, Allison M Ezzat, Ju Young Yoo, Clayon B Hamilton, Linda C Li. Originally published in JMIR Mhealth and Uhealth (http://mhealth.jmir.org), 09.08.2018.

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Conflict of interest statement

Conflicts of Interest: None declared.

Figures

Figure 1
Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow chart.

Figure 2
Figure 2

Percentage error distribution by sample size. Top: Step count in controlled settings. The blue oval indicates extreme outliers (n=4 comparisons). Bottom: Energy expenditure in controlled settings. Solid blue lines indicate mean error estimation. Dotted blue lines indicate 95% CI.

Figure 3
Figure 3

Step count percentage error in controlled settings. Speed (jog, normal, self-paced, slow, very slow) by body placement (torso, wrist, ankle) of the Fitbit device. Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Gray shading indicates ±3% measurement error.

Figure 4
Figure 4

Step count percentage error in controlled settings. Body placement (torso, wrist, ankle) of the Fitbit device by speed (jog, normal, self-paced, slow, very slow). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Gray shading indicates ±3% measurement error.

Figure 5
Figure 5

Step count percentage error in controlled settings. Body motion (normal, constrained, exaggerated, variable) by speed (jog, normal, self-paced, slow, very slow). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal).

Figure 6
Figure 6

Energy expenditure percentage error in controlled settings. Activity versus rest by body placement (torso, wrist). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Triangles indicate measurement by direct calorimetry. Gray shading indicates ±3% measurement error.

Figure 7
Figure 7

Energy expenditure percentage error in controlled settings. Body placement (torso, wrist) by speed (jog, normal, self-paced, slow, very slow). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Triangles indicate measurement by direct calorimetry. Gray shading indicates ±3% measurement error.

Figure 8
Figure 8

Energy expenditure percentage error in controlled settings. Speed (jog, normal, slow, self-paced, very slow) by body placement (torso, wrist). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Triangles indicate measurement by direct calorimetry. Gray shading indicates ±3% measurement error.

Figure 9
Figure 9

Energy expenditure percentage error in controlled settings. Motion limitations (normal, constrained, exaggerated, variable) by speed (jog, normal, self-paced, slow, very slow). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Triangles indicate measurement by direct calorimetry. Gray shading indicates ±3% measurement error.

Figure 10
Figure 10

Energy expenditure percentage error in controlled settings. Type of ambulation (continuous no incline, continuous incline, intermittent) by body placement (torso, wrist). Dark lines indicate mean (horizontal). Dashed lines indicate median (horizontal). Triangles indicate measurement by direct calorimetry. Gray shading indicates ±3% measurement error.

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