Methodology State-of-the-art workshop: Choosing the target difference (“effect size”) for a randomised controlled trial

随机对照试验（RCT）被认为是评估比较临床疗效和有效性的最佳研究设计。样本量计算确保研究有合理的机会实现其预先设定的目标：需要在被偶然误导的可能性（治疗之间没有真正的差异）和即使其中一种治疗确实更好也无法识别差异的风险之间做出妥协。“目标差值”是RCT设计用于可靠调查的差值的大小。它通常也被称为试验“效应量”。关键的问题是，统计上发现的特定差异是否具有实际意义。从科学和伦理的角度来看，选择一个适当的目标差异是至关重要的——指定一个太小的目标差异可能是对资源的浪费（也许是不道德的）使用，而太大可能导致一个重要的差异被忽视。此外，由此产生的小规模研究不会产生可靠的证据。尽管有许多不同的方法可用于选择目标差，但很少在实践中经常使用。该项目将：1；检讨现有的指引；2. 确定实践中关键方法的发展或变化；3. 确定所需指导的范围；4. 为选择和报告目标差异（效应大小）提供结构化指导

Randomised controlled trials (RCT) are considered the optimal study design to assess comparative clinical efficacy and effectiveness. A sample size calculation ensures the study has a reasonable chance to achieve its pre-specified objectives: A compromise is required between the possibility of being misled by chance (there is no true difference between treatments) and the risk of not identifying a difference even when one of the treatments is truly superior. The “target difference” is the size of the difference the RCT is designed to reliably investigate. It is also commonly referred to as the trial “effect size”. The critical question is whether a particular difference detected statistically, is of any practical interest. From a scientific and ethical standpoint, selecting an appropriate targeted difference is of crucial importance - specifying too small a target difference could be a wasteful (and perhaps unethical) use of resources, and too large could lead to an important difference being overlooked. Furthermore, the resultant undersized study will not produce reliable evidence.Despite there being many different approaches available to choose the target difference, few are used regularly in practice. The project will: 1. Review the existing guidance; 2. Identify key methodological developments or changes in practice; 3. Determine the scope of the guidance required; 4. Produce structured guidance for choosing and reporting the target difference (effect size)