J Phys Act Health. 2018 Sep 1;15(9):651-660. doi: 10.1123/jpah.2017-0375. Epub 2018 May 10.
Direct observation protocols may introduce variability in physical activity estimates.
Thirty-five physical education lessons were video recorded and coded using the System for Observing Fitness Instruction Time (SOFIT). A multistep process examined variability in moderate to vigorous physical activity (MVPA%; walking + vigorous/total scans). Initially, per-SOFIT protocol MVPA% (MVPA%SOFIT) estimates were produced for each lesson. Second, true MVPA% (mean MVPA% of all students using all observations, MVPA%true) estimates were calculated. Third, MVPA% (MVPA%perm) was calculated based on all permutations of students and observation order. Fourth, physical education lessons were divided into 2 groups with 5 lessons from each group randomly selected 10,000 times. Group MVPA%perm differences between the 10 selected lessons were compared with the MVPA%true difference between group 1 and group 2.
Across all lessons, 10,212,600 permutations were possible (average 291,789 combinations per lesson; range = 73,440-570,024). Across lessons, the average absolute difference between MVPA%true and MVPA%SOFIT estimates was ±4.8% (range = 0.1%-17.5%). Permutations, based on students selected and observation order, indicated that the mean range of MVPA%perm estimates was 41.6% within a lesson (range = 29.8%-55.9%). Differences in MVPA% estimates between the randomly selected groups of lessons varied by 32.0%.
MVPA% estimates from focal child observation should be interpreted with caution.
直接观察方案可能会使身体活动估计值产生变异性。
对 35 节体育课进行录像并使用体力活动教学观察时间系统（SOFIT）进行编码。采用多步骤流程，对中等到剧烈身体活动（MVPA%；行走+剧烈/总扫描）的变异性进行检查。首先，为每节课生成基于 SOFIT 方案的 MVPA%（MVPA%SOFIT）估计值。其次，计算真实 MVPA%（所有学生使用所有观察结果的平均 MVPA%，MVPA%true）估计值。然后，基于学生和观察顺序的所有排列，计算 MVPA%（MVPA%perm）。最后，将体育课分为两组，每组随机抽取 5 节课，进行 10000 次抽样。将 10 节选定课程之间的组 MVPA%perm 差异与组 1 和组 2 之间的 MVPA%true 差异进行比较。
在所有课程中，可能有 10212600 种排列（平均每节课 291789 种组合；范围=73440-570024）。在所有课程中，MVPA%true 和 MVPA%SOFIT 估计值之间的平均绝对差异为±4.8%（范围=0.1%-17.5%）。基于选定学生和观察顺序的排列表明，一节课内 MVPA%perm 估计值的平均范围为 41.6%（范围=29.8%-55.9%）。随机选择的课程组之间的 MVPA%估计值差异为 32.0%。
应谨慎解释来自重点儿童观察的 MVPA%估计值。
