School-level intraclass correlation for physical activity in sixth grade girls
School-level intraclass correlation for physical activity in sixth grade girls
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DOI：
10.1249/01.mss.0000218188.57274.91
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发表时间：
2006-05-01
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影响因子：
--
通讯作者：
Yang, Song
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文献类型：
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作者：
Murray, David M.;Stevens, June;Yang, Song
目的：青春期女孩活动试验(TAAG)是一项团体随机试验(GRT)，旨在减少中学女生中中等到剧烈体力活动(MVPA)的通常下降。我们从TAAG对六年级女生的基线调查中报告了MVPA的学校水平组内相关性(ICC)，并描述了数据收集计划与ICC之间的关系。方法：6个地点每个地点招收6所学校，每所学校随机抽取60名六年级女生，参与率为74.2%。根据测量开始的日期，女孩们被分成不同的波，要求她们佩戴Actigraph加速计6d。偶尔遗漏的数据被归罪，每30名S中超过1500人的数据被视为MVPA，转换为代谢当量(METS)，并在早上6点到午夜的时间相加，提供每18小时一天的MET分钟数。采用混合模型回归方法估计ICC。结果：单波与三波相比，学校水平的IC值较高(例如，0.057比0.022)，平日与周末相比，学校水平的IC值较高(例如，0.024比0.012)。在新的试验中，一些时间表(例如，给予三波和6天的88%)的功率将比其他时间表(例如，给予一波和仅周二的23%)更大。结论：数据收集的时间安排对MVPA的ICC有很大影响。反过来，这会对干预效果的标准误差和功率产生显著影响。在计划一项新的研究时，研究人员将需要考虑ICC的预期规模以及与他们的数据收集计划相关的MVPA估计的有效性。
Purpose: The Trial for Activity in Adolescent Girls (TAAG) is a group-randomized trial (GRT) to reduce the usual decline in moderate to vigorous physical activity (MVPA) among middle school girls. We report the school-level intraclass correlation (ICC) for MVPA from the TAAG baseline survey of sixth grade girls and describe the relationship between the schedule of data collection and the ICC. Methods: Each of six sites recruited six schools and randomly selected 60 sixth grade girls from each school: 74.2% participated. Girls were grouped in waves defined by the date measurements began and asked to wear an Actigraph accelerometer for 6 d. Occasional missing data were replaced by imputation, and counts above 1500 per 30 s were treated as MVPA, converted into metabolic equivalents (METs), and summed over 6 a.m.-midnight to provide MET-minutes per 18-h day. Mixed-model regression was used to estimate ICC. Results: The school-level ICC were higher when estimated from a single wave compared with three waves (e.g., 0.057 vs 0.022) and across weekdays compared with weekend days (e.g.. 0.024 vs 0.012). Power in a new trial would be greater with some schedules (e.g., 88% given three waves and 6 d) than with others (e.g., 23% given one wave and Tuesday only). Conclusions: The schedule of data collection can have a dramatic effect on the ICC for MVPA. In turn, this can have a dramatic effect on the standard error for an intervention effect and on power. Investigators will need to consider the expected magnitude of the ICC and the validity of the MVPA estimates associated with their data collection schedule in planning a new study.