Darcy Ummels

30 | Chapter 2 between the tracker and gold standard varied from –29.7 (SD 155.10) for the Fitbit One to 252.4 (SD 129.0) for the Digi ‐ Walker CW ‐ 700. Overall, data distribution showed a wide range of observations for all activity trackers. There were no differences found per chronic disease compared to the whole population. Scatter plots of the Fitbit One, Digi ‐ Walker CW ‐ 700, and Activ8 are presented in Figures 2.1 ‐ 2.3 to give examples of data distribution. Table 2.4 Descriptive statistics of step count by activity tracker compared to the gold standard. Activity tracker Number of participants Average mean difference in step count (SD) a Average median difference in step count (25 to 75 percentile) a Limits of agreement (lower bound– upper bound) Accupedo 50 –176.3 (132.1) –174.5 (–251.0 to –102.5) –435.2 to 82.7 Activ8 62 107.3 (251.9) 126.0 (30.5 to 243.5) –471.3 to 721.0 Digi ‐ Walker CW ‐ 700 52 –284.5 (129.0) –253.0 (–383.0 to –169.0) –537.4 to –31.7 Fitbit Flex 47 –93.5 (126.7) –111.0 (–167.0 to 3.0) –326.9 to 123.7 Lumoback 51 –178.5 (96.0) –168.0 (–205.5 to –117,0) –366.9 to 9.3 Moves 48 –146.6 (216.3) –215.0 (–279.5 to –89.3) –570.5 to 277.4 Fitbit One 49 –29.7 (155.1) –8.0 (–160.0 to 128.0) –367.8 to 308.6 UP24 49 –252.4 (104.7) –266.0 (–327.0 to –176.5) –457.7 to –47.2 Walking Style X 50 –204.4 (117.7) –206.5 (–256.0 to –105.0) –438.0 to 27.2 a Activity tracker minus gold standard. Figure 2.1 Scatterplot of the number of steps counted by Fitbit One and the gold standard.