Puffer Suezann, Torgerson David, Watson Judith
York Trials Unit, Department of Health Sciences, York University, York YO10 5DD.
BMJ. 2003 Oct 4;327(7418):785-9. doi: 10.1136/bmj.327.7418.785.
To examine the prevalence of a risk of bias associated with the design and conduct of cluster randomised controlled trials among a sample of recently published studies.
Retrospective review of cluster randomised trials published in the BMJ, Lancet, and New England Journal of Medicine from January 1997 to October 2002.
Prevalence of secure randomisation of clusters, identification of participants before randomisation (to avoid foreknowledge of allocation), differential recruitment between treatment arms, differential application of inclusion and exclusion criteria, and differential attrition.
Of the 36 trials identified, 24 were published in the BMJ,11 in the Lancet, and a single trial in the New England Journal of Medicine. At the cluster level, 15 (42%) trials provided evidence for secure allocation and 25 (69%) used stratified allocation. Few trials showed evidence of imbalance at the cluster level. However, some evidence of susceptibility to risk of bias at the individual level existed in 14 (39%) studies.
Some recently published cluster randomised trials may not have taken adequate precautions to guard against threats to the internal validity of their design.
在一组近期发表的研究样本中，考察与整群随机对照试验的设计和实施相关的偏倚风险的发生率。
对1997年1月至2002年10月发表在《英国医学杂志》《柳叶刀》和《新英格兰医学杂志》上的整群随机试验进行回顾性分析。
整群的可靠随机化发生率、随机化前对参与者的识别（以避免知晓分配情况）、治疗组间的差异招募、纳入和排除标准的差异应用以及差异失访。
在确定的36项试验中，24项发表于《英国医学杂志》，11项发表于《柳叶刀》，1项发表于《新英格兰医学杂志》。在整群水平上，15项（42%）试验提供了可靠分配的证据，25项（69%）采用了分层分配。很少有试验显示在整群水平上存在不平衡的证据。然而，14项（39%）研究存在一些个体水平上易受偏倚风险影响的证据。
一些近期发表的整群随机试验可能未采取足够的预防措施来防范对其设计内部效度的威胁。
