Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK.
The National Institute for Health Research, Applied Research Collaboration West (NIHR ARC West), University Hospitals Bristol and Weston NHS Foundation Trust, Bristol, UK.
BMC Med Res Methodol. 2024 Aug 9;24(1):179. doi: 10.1186/s12874-024-02290-7.
Randomised, cluster-based study designs in schools are commonly used to evaluate children's physical activity interventions. Sample size estimation relies on accurate estimation of the intra-cluster correlation coefficient (ICC), but published estimates, especially using accelerometry-measured physical activity, are few and vary depending on physical activity outcome and participant age. Less commonly-used cluster-based designs, such as stepped wedge designs, also need to account for correlations over time, e.g. cluster autocorrelation (CAC) and individual autocorrelation (IAC), but no estimates are currently available. This paper estimates the school-level ICC, CAC and IAC for England children's accelerometer-measured physical activity outcomes by age group and gender, to inform the design of future school-based cluster trials.
Data were pooled from seven large English datasets of accelerometer-measured physical activity data between 2002-18 (> 13,500 pupils, 540 primary and secondary schools). Linear mixed effect models estimated ICCs for weekday and whole week for minutes spent in moderate-to-vigorous physical activity (MVPA) and being sedentary for different age groups, stratified by gender. The CAC (1,252 schools) and IAC (34,923 pupils) were estimated by length of follow-up from pooled longitudinal data.
School-level ICCs for weekday MVPA were higher in primary schools (from 0.07 (95% CI: 0.05, 0.10) to 0.08 (95% CI: 0.06, 0.11)) compared to secondary (from 0.04 (95% CI: 0.03, 0.07) to (95% CI: 0.04, 0.10)). Girls' ICCs were similar for primary and secondary schools, but boys' were lower in secondary. For all ages, combined the CAC was 0.60 (95% CI: 0.44-0.72), and the IAC was 0.46 (95% CI: 0.42-0.49), irrespective of follow-up time. Estimates were higher for MVPA vs sedentary time, and for weekdays vs the whole week.
Adequately powered studies are important to evidence effective physical activity strategies. Our estimates of the ICC, CAC and IAC may be used to plan future school-based physical activity evaluations and were fairly consistent across a range of ages and settings, suggesting that results may be applied to other high income countries with similar school physical activity provision. It is important to use estimates appropriate to the study design, and that match the intended study population as closely as possible.
在学校中，基于随机分组的研究设计常用于评估儿童的身体活动干预效果。样本量估计依赖于对组内相关系数（ICC）的准确估计，但发表的估计值很少，尤其是使用加速度计测量的身体活动，而且因身体活动结果和参与者年龄而异。不太常用的基于群组的设计，如阶梯式楔形设计，也需要考虑随时间的相关性，例如群组自相关（CAC）和个体自相关（IAC），但目前尚无估计值。本文旨在为未来的基于学校的群组试验设计提供信息，通过按年龄组和性别估计英格兰儿童加速度计测量的身体活动结果的学校水平 ICC、CAC 和 IAC。
从 2002-18 年期间七个英国大型数据集（>13500 名小学生，540 所小学和中学）中汇总了加速度计测量的身体活动数据。使用线性混合效应模型估计了不同性别和不同年龄组的工作日和整个星期的中等到剧烈体力活动（MVPA）和久坐时间的 ICC。通过汇总纵向数据估计了 CAC（1252 所学校）和 IAC（34923 名学生）。
与中学相比，小学的工作日 MVPA 学校内相关系数更高（从 0.07（95%CI：0.05，0.10）到 0.08（95%CI：0.06，0.11））（从 0.04（95%CI：0.03，0.07）到 0.04（95%CI：0.04，0.10））。小学和中学的女孩 ICC 相似，但中学男孩的 ICC 较低。所有年龄段的 CAC 均为 0.60（95%CI：0.44-0.72），IAC 为 0.46（95%CI：0.42-0.49），与随访时间无关。MVPA 与久坐时间的 CAC 和 IAC 均高于工作日与整个星期。
有力的研究对于证明有效的身体活动策略很重要。我们对 ICC、CAC 和 IAC 的估计值可用于计划未来的基于学校的身体活动评估，并且在各种年龄和环境中相当一致，这表明结果可能适用于其他具有类似学校身体活动提供的高收入国家。重要的是，要使用与研究设计和研究对象最匹配的估计值。
