Department of Preventive Medicine and Public Health, Tokyo Medical University, Shinjuku-ku, Japan.
Department of Social and Behavioral Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, United States.
JMIR Mhealth Uhealth. 2019 Jan 9;7(1):e10418. doi: 10.2196/10418.
Smartphones have great potential for monitoring physical activity. Although a previous laboratory-based study reported that smartphone apps were accurate for tracking step counts, little evidence on their accuracy in free-living conditions currently exists.
We aimed to investigate the accuracy of step counts measured using iPhone in the real world.
We recruited a convenience sample of 54 adults (mean age 31 [SD 10] years) who owned an iPhone and analyzed data collected in 2016 and 2017. Step count was simultaneously measured using a validated pedometer (Kenz Lifecorder) and the iPhone. Participants were asked to carry and use their own iPhones as they typically would while wearing a pedometer on the waist for 7 consecutive days during waking hours. To assess the agreement between the two measurements, we calculated Spearman correlation coefficients and prepared a Bland-Altman plot.
The mean step count measured using the iPhone was 9253 (3787) steps per day, significantly lower by 12% (1277/10,530) than that measured using the pedometer, 10,530 (3490) steps per day (P<.001). The Spearman correlation coefficient between devices was 0.78 (P<.001). The largest underestimation of steps by the iPhone was observed among those who reported to have seldom carried their iPhones (seldom carry: mean -3036, SD 2990, steps/day; sometimes carry: mean -1424, SD 2619, steps/day; and almost always carry: mean -929, SD 1443, steps/day; P for linear trend=.08).
Smartphones may be of practical use to individuals, clinicians, and researchers for monitoring physical activity. However, their data on step counts should be interpreted cautiously because of the possibility of underestimation due to noncarrying time.
智能手机在监测身体活动方面具有很大的潜力。虽然之前有一项基于实验室的研究报告称，智能手机应用程序在跟踪步数方面是准确的，但目前几乎没有关于其在自由生活条件下准确性的证据。
我们旨在研究 iPhone 在现实世界中测量步数的准确性。
我们招募了 54 名成年人（平均年龄 31 [SD 10] 岁）作为便利样本，他们都拥有一部 iPhone，并分析了 2016 年和 2017 年的数据。使用经过验证的计步器（Kenz Lifecorder）和 iPhone 同时测量步数。参与者被要求在佩戴腰部计步器的情况下连续 7 天在清醒时携带并使用他们自己的 iPhone，就像他们通常那样。为了评估两种测量方法之间的一致性，我们计算了 Spearman 相关系数并准备了 Bland-Altman 图。
使用 iPhone 测量的平均步数为每天 9253（3787）步，比使用计步器测量的每天 10530（3490）步低 12%（1277/10530）（P<.001）。两种设备之间的 Spearman 相关系数为 0.78（P<.001）。iPhone 对步数的最大低估发生在报告很少携带 iPhone 的人（很少携带：平均 -3036，SD 2990，步/天；有时携带：平均 -1424，SD 2619，步/天；几乎总是携带：平均 -929，SD 1443，步/天；线性趋势 P 值=0.08）。
智能手机可能对个人、临床医生和研究人员监测身体活动具有实际用途。然而，由于非携带时间的可能性，其计步数据的解释应谨慎，因为可能存在低估的情况。
