Design, Identification, and Sensitivity Analysis for Patient Preference Trials

Social and medical scientists are often concerned that the external validity of experimental results may be compromised because of heterogeneous treatment effects. If a treatment has different effects on those who would choose to take it and those who would not, the average treatment effect estimated in a standard randomized controlled trial (RCT) may give a misleading picture of its impact outside of the study sample. Patient preference trials (PPTs), where participants’ preferences over treatment options are incorporated in the study design, provide a possible solution. In this paper, we provide a systematic analysis of PPTs based on the potential outcomes framework of causal inference. We propose a general design for PPTs with multi-valued treatments, where participants state their preferred treatments and are then randomized into either a standard RCT or a self-selection condition. We derive nonparametric sharp bounds on the average causal effects among each choice-based subpopulation of participants under the proposed design. We also propose a sensitivity analysis for the violation of the key ignorability assumption sufficient for identifying the target causal quantity. The proposed design and methodology are illustrated with an original study of partisan news media and its behavioral impact. Supplementary materials for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement.社会科学与医学领域的学者常常担忧，异质性处理效应可能会损害实验结果的外部有效性。若某一处理对自愿选择接受该处理的群体与不愿接受该处理的群体产生的效果存在差异，那么标准随机对照试验（randomized controlled trial, RCT）中估计的平均处理效应，可能会对该处理在研究样本之外的实际影响给出误导性的描述。患者偏好试验（Patient preference trials, PPTs）将参与者对处理方案的偏好纳入研究设计，为此类问题提供了可行的解决路径。 本文基于因果推断的潜在结果框架，对患者偏好试验开展了系统性分析。我们针对多值处理场景提出了一种通用的患者偏好试验设计：参与者先陈述自身偏好的处理方案，随后被随机分配至标准随机对照试验组或自我选择组。基于该设计，我们推导得到了各基于选择的参与者子群体的平均因果效应的非参数紧界。此外，我们还针对识别目标因果量所需的关键可忽略性假设的违背情况，提出了敏感性分析方法。 我们通过一项针对党派新闻媒体及其行为影响的原创性研究，对所提出的试验设计与分析方法进行了实例演示。本文的补充材料（包含可用于重现该研究的标准化材料说明）可通过在线补充资源获取。