CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
J Clin Epidemiol. 2013 Sep;66(9):948-54. doi: 10.1016/j.jclinepi.2013.03.019. Epub 2013 Jun 21.
Differential attrition is regarded as a major threat to the internal validity of a randomized controlled trial (RCT). This study identifies the degree of differential attrition in RCTs covering a broad spectrum of clinical areas and factors that are related to this.
A PubMed search was conducted to obtain a random sample of 100 RCTs published between 2008 and 2010 in journals from the ISI Web of Knowledge(SM) category of medicine, general and internal. Eligibility criteria for selecting studies were primary publications of two-arm parallel randomized clinical trials, containing human participants and one or multiple follow-up measurements whose availability depended on the patients' willingness to participate.
A significant amount of differential attrition was observed in 8% of the trials. The average differential attrition rate was 0.99 (95% confidence interval: 0.97-1.01), indicating no general difference in attrition rates between intervention and control groups. Moreover, no indication of heterogeneity was found, suggesting that the occurrence of differential attrition in the published literature is mostly a chance finding, unrelated to any particular design factors.
Differential attrition did not generally occur in RCTs covering a broad spectrum of clinical areas within general and internal medicine.
差异失访被认为是随机对照试验（RCT）内部有效性的主要威胁。本研究旨在确定涵盖广泛临床领域的 RCT 中差异失访的程度，以及与差异失访相关的因素。
通过 PubMed 检索，从 ISI Web of Knowledge（SM）医学、普通和内科类别中的期刊中获取了 100 篇 2008 年至 2010 年发表的 RCT 的随机样本。研究选择的标准为：双臂平行随机临床试验的主要出版物，包含人类参与者和一个或多个随访测量，其可用性取决于患者参与的意愿。
在 8%的试验中观察到了大量的差异失访。平均差异失访率为 0.99（95%置信区间：0.97-1.01），表明干预组和对照组之间的失访率没有一般差异。此外，没有发现异质性的迹象，这表明发表文献中的差异失访大多是偶然发现的，与任何特定的设计因素无关。
在涵盖普通和内科广泛临床领域的 RCT 中，差异失访一般不会发生。
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