Objectives:

Focused on the accelerometer-determined physical activity and sedentary time metrics in 9–11-year-old children, we sought to determine the following: (i) number of days that are necessary to achieve reliable estimates (G⩾0.8); (ii) proportion of variance attributed to different facets (participants and days) of reliability estimates; and (iii) actual reliability of data as collected in The International Study of Childhood Obesity, Lifestyle and Environment (ISCOLE).

Methods:

The analytical sample consisted of 6025 children (55% girls) from sites in 12 countries. Physical activity and sedentary time metrics measures were assessed for up to 7 consecutive days for 24 h per day with a waist-worn ActiGraph GT3X+. Generalizability theory using R software was used to investigate the objectives i and ii. Intra-class correlation coefficients (ICC) were computed using SAS PROC GLM to inform objective iii.

Results:

The estimated minimum number of days required to achieve a reliability estimate of G⩾0.8 ranged from 5 to 9 for boys and 3 to 11 for girls for light physical activity (LPA); 5 to 9 and 3 to 10, for moderate-to-vigorous physical activity (MVPA); 5 to 10 and 4 to 10 for total activity counts; and 7 to 11 and 6 to 11 for sedentary time, respectively. For all variables investigated, the ‘participant’ facet accounted for 30–50% of the variability, whereas the ‘days’ facet accounted for ⩽5%, and the interaction (P × D) accounted for 50–70% of the variability. The actual reliability for boys in ISCOLE ranged from ICCs of 0.78 to 0.86, 0.73 to 0.85 and 0.72 to 0.86 for LPA, MVPA and total activity counts, respectively, and 0.67 to 0.79 for sedentary time. The corresponding values for girls were 0.80–0.88, 0.70–0.89, 0.74–0.86 and 0.64–0.80.

Conclusions:

It was rare that only 4 days from all participants would be enough to achieve desirable reliability estimates. However, asking participants to wear the device for 7 days and requiring ⩾4 days of data to include the participant in the analysis might be an appropriate approach to achieve reliable estimates for most accelerometer-derived metrics.

中文翻译：

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加速度计确定的体育活动和久坐行为在学龄儿童中的可靠性：一项12国研究

目标：

专注于加速计确定身体活动和在9-11岁的儿童久坐时间指标，我们试图确定如下：天是必要的，以实现可靠的估计（（i）的数量摹⩾ 0.8）; （ii）归因于可靠性估计的不同方面（参与者和天数）的差异比例；（iii）《国际儿童肥胖，生活方式和环境研究》（ISCOLE）中收集的数据的实际可靠性。

方法：

分析样本包括来自12个国家/地区的6025名儿童（55％的女孩）。使用腰围的ActiGraph GT3X +，每天最多连续7天每天进行24小时的体育锻炼和久坐时间指标评估。使用R软件的概化理论用于研究目标i和ii。使用SAS PROC GLM计算类内相关系数（ICC），以告知目标iii。

结果：

天的估计最小数目需要达到的可靠性估计值G ^ ⩾ 0.8男孩女孩为轻体力活动（LPA）介于5至9和3至11; 5至9和3至10，用于中度至剧烈的体育锻炼（MVPA）；总活动计数为5到10和4到10；久坐时间分别为7至11和6至11。对于所有调查的变量，“参与者”方面占变异性的30％至50％，而“天”方面占⩽5％，而交互作用（P×D）占变异性的50–70％。ISCOLE中男孩的实际可靠性分别为LPA，MVPA和总活动计数的ICC为0.78至0.86、0.73至0.85和0.72至0.86，而久坐时间则为0.67至0.79。女孩的相应值分别为0.80-0.88、0.70-0.89、0.74-0.86和0.64-0.80。

结论：

很少有来自所有参与者的4天足以达到理想的可靠性估计。但是，要求参与者佩戴设备7天，并需要⩾4天的数据才能将参与者包括在分析中，这可能是一种合适的方法，可对大多数加速度计得出的指标进行可靠的估算。