Prentice Ross
Fred Hutchinson Cancer Research Center and University of Washington, USA.
Int J Biostat. 2011 Aug 13;7(1):1-15. doi: 10.2202/1557-4679.1359.
Pearl (2011) posed the question of whether confinement of clinical trial analyses involving post-randomization variables to the principal stratum "framework" of Frangakis and Rubin (2002) unduly restricts the scientific questions that can be asked. Frangakis and Rubin illustrated their proposal through examples involving compliance, mediation, and surrogacy. Here the utility of the principal stratum framework, and the potential outcomes formulation from which it derives, are considered for these topics in the specific setting of the Women's Health Initiative randomized, placebo controlled trials of postmenopausal hormone therapy. It is argued that the essential issues related to study reliability and causal interpretation involve the avoidance of context-specific biases that are typically not closely related to whether or not treatment effects have a representation in terms of potential outcomes contrasts. Also, while the questions posed within principal strata may be of interest, some key questions in the hormone therapy setting would not be addressed if restricted to contrasts within principal strata.
珀尔（2011年）提出了这样一个问题：将涉及随机化后变量的临床试验分析局限于弗兰加基斯和鲁宾（2002年）的主要层“框架”，是否会过度限制可提出的科学问题。弗兰加基斯和鲁宾通过涉及依从性、中介作用和替代指标的例子阐述了他们的提议。在此，在女性健康倡议绝经后激素治疗的随机、安慰剂对照试验的特定背景下，针对这些主题考虑主要层框架的效用及其所源自的潜在结果表述。有人认为，与研究可靠性和因果解释相关的关键问题涉及避免特定背景下的偏差，这些偏差通常与治疗效果是否能以潜在结果对比的形式呈现并无紧密关联。此外，虽然主要层内提出的问题可能会令人感兴趣，但如果局限于主要层内的对比，激素治疗背景下的一些关键问题将无法得到解决。
