Pragmatic trials evaluate the effectiveness of health interventions compared to usual care in real-world settings. Confounding arises in a pragmatic trial if the study intervention affects how scarce resources are allocated between patients in the intervention and comparison groups. There is currently no recognition of this source of bias - which I term "confounding by scarcity" - in the medical literature. In this article, I examine what causes confounding by scarcity and how it might affect outcomes in trials of patient navigation, physiological alarms, and elective induction of labor. I also suggest ways to detect confounding by scarcity, design trials that avoid it, and modify clinical trial guidelines to address this unrecognized source of bias.

翻译：务实试验在真实世界环境中评估健康干预措施相较于常规护理的效果。如果研究干预措施影响到稀缺资源在干预组与对照组患者之间的分配方式，则会在务实试验中产生混杂。目前医学文献中尚未认识到这种偏倚来源——我将其称为"稀缺性导致的混杂"。本文探讨了稀缺性导致混杂的原因，以及它如何影响患者导航、生理警报和择期引产等试验的结果。同时，我还提出了检测稀缺性导致的混杂的方法、设计避免该问题的试验策略，以及修改临床试验指南以应对这一未被认识的偏倚来源的可行建议。