Sichieri Rosely, Cunha Diana Barbosa
Department of Epidemiology, Institute of Social Medicine, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
Obes Facts. 2014;7(4):221-32. doi: 10.1159/000363438. Epub 2014 Jun 28.
BACKGROUND/AIMS: Cluster designs favor unbalanced baseline measures. The aim of the present study was to determine the frequency of unbalanced baseline BMI on school-based randomized controlled trials (RCT) aimed at obesity reduction and to evaluate the analysis strategies. We hypothesized that the adjustment of unbalanced baseline measures may explain the great discrepancy among studies.
The source of data was the Medline database content from January 1995 until May 2012. Our search strategy combined key words related to school-based interventions with such related to weight and was not limited by language. The participants' ages were restricted to 6-18 years.
We identified 146 school-based studies on obesity prevention (or overweight or excessive weight change). Of the 146 studies, 36 were retained for the analysis after excluding reviews, feasibility studies, other outcomes, and repeated publications. 13 (35%) of the reviewed studies had statistically significant (p < 0.05) unbalanced measures of BMI at baseline. 11 studies with BMI balanced at baseline adjusted for the baseline BMI, whereas no baseline adjustment was applied to the 5 unbalanced studies.
Adjustment for the baseline BMI is frequently done in cluster randomized studies, and there is no standardization for this procedure. Thus, procedures that disentangle the effects of group, time and changes in time, such as mixed effects models, should be used as standard methods in school-based studies on the prevention of weight gain.
背景/目的：整群设计有利于不均衡的基线测量。本研究的目的是确定在校随机对照试验（RCT）中旨在减轻肥胖的不均衡基线体重指数（BMI）的频率，并评估分析策略。我们假设对不均衡基线测量的调整可能解释了研究之间的巨大差异。
数据来源是1995年1月至2012年5月的Medline数据库内容。我们的检索策略将与在校干预相关的关键词与与体重相关的关键词相结合，且不受语言限制。参与者年龄限制在6至18岁。
我们确定了146项关于肥胖预防（或超重或体重过度变化）的在校研究。在这146项研究中，排除综述、可行性研究、其他结局和重复发表的研究后，保留36项进行分析。在纳入综述的研究中，13项（35%）在基线时BMI测量存在统计学显著（p<0.05）的不均衡。11项基线BMI均衡的研究对基线BMI进行了调整，而5项不均衡研究未进行基线调整。
在整群随机研究中经常对基线BMI进行调整，且该程序没有标准化。因此，在在校预防体重增加的研究中，应将诸如混合效应模型等能够区分组效应、时间效应和时间变化的程序作为标准方法使用。
