Confounding by Scarcity: An Overlooked Source of Bias in Pragma@c Trials
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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.
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