School-level intraclass correlation for physical activity in adolescent girls
School-level intraclass correlation for physical activity in adolescent girls
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DOI：
10.1249/01.mss.0000126806.72453.1c
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发表时间：
2004-05-01
期刊：
影响因子：
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通讯作者：
Conway, TL
中科院分区：
文献类型：
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作者：
Murray, DM;Catellier, DJ;Conway, TL
目的：青春期女孩活动试验（TAAG）是一项多中心随机分组试验，旨在减少中学女孩中中度至剧烈体力活动（MVPA）的通常下降。在分组随机试验中，组水平的组内相关性（ICC）与功效有很强的反比关系，需要对ICC进行良好的估计以确定样本量。因此，我们进行了一项子研究，以估计学校一级的ICC强度加权分钟MVPA使用加速度计测量。研究方法：为了估计ICC，六个地点中的每一个都招募了两所学校，并从每所学校随机选择了45名八年级女生; 80.7%的人参加了。每个女孩都戴了一个Activograph加速度计7天。每半分钟超过1500个计数的读数计为MVPA。将这些计数转换为代谢当量（MET），并在上午6点至午夜期间求和，以提供MVPA每18小时的MET分钟数。还计算了每18小时一天的MVPA分钟数，忽略MET值。结果如下：MVPA分钟数的未校正学校水平ICC为0.0205（95%CI：-0.0079，0.1727），MVPA MET分钟数的未校正学校水平ICC为0.0045（95%CI：-0.0147，0.1145）。年龄和BMI的调整没有可测量的影响，而种族的调整降低了ICC; MVPA分钟的调整值为0.0175（95% CI：-0.0092，0.1622），MVPA MET分钟的调整值为0.0000（95% CI：-0.0166，0.0968）。这些信息被用来计算学校和女孩的数量需要TAAG有90%的权力，以检测减少50%的下降MVPA的met分钟的六年级和八年级之间。结论：结果要求TAAG的36所学校，每所学校邀请120名女孩进行测量，最低参与率为90%。
Purpose: The Trial for Activity in Adolescent Girls (TAAG) is a multi-center group-randomized trial to reduce the usual decline in moderate to vigorous physical activity (MVPA) among middle-school girls. In group-randomized trials, the group-level intraclass correlation (ICC) has a strong inverse relationship to power and a good estimate of ICC is needed to determine sample size. As a result, we conducted a substudy to estimate the school-level ICC for intensity-weighted minutes of MVPA measured using an accelerometer. Methods: To estimate the ICC, each of six sites recruited two schools and randomly selected 45 eighth grade girls from each school; 80.7% participated. Each girl wore an Actigraph accelerometer for 7 d. Readings above 1500 counts per half minute were counted as MVPA. These counts were converted into metabolic equivalents (MET) and summed over 6 a.m. to midnight to provide MET-minutes per 18-h day of MVPA. Minutes of MVPA per 18-h day also were calculated ignoring the MET value. Results: The unadjusted school-level ICC for minutes of MVPA was 0.0205 (95%CI: -0.0079, 0.1727) and for MET-minutes of MVPA was 0.0045 (95% CI: -0.0147, 0.1145). Adjustment for age and BMI had no measurable effect, whereas adjustment for ethnicity reduced both ICC; adjusted values were 0.0175 (95% CI: -0.0092, 0.1622) for minutes of MVPA and 0.0000 (95% CI: -0.0166, 0.0968) for MET-minutes of MVPA. This information was used to calculate the number of schools and girls needed for TAAG to have 90% power to detect a 50% reduction in the decline of MET-minutes of MVPA between sixth and eighth grade. Conclusions: The results called for 36 schools in TAAG, with 120 girls invited for measurements at each school, and a minimum participation rate of 90%.