Controls, belief updating, and bias in medical RCTs

• 成果类型: Article
• 署名作者: Chemla, Gilles; Hennessy, Christopher A.
• 署名单位: Imperial College London; Centre for Economic Policy Research - UK; Centre for Economic Policy Research - UK; University of London; London Business School; University of London; London Business School
• 刊物名称: JOURNAL OF ECONOMIC THEORY
• ISSN/ISSBN: 0022-0531
• DOI: 10.1016/j.jet.2019.07.016
• 发表日期: 2019
• 关键词: Belief updating; Medical RCTs; BIAS; Control; Treatment

摘要

We develop a formal model of placebo effects. If subjects in seemingly-ideal single-stage RCTs update beliefs about breakthroughs based upon personal physiological responses, mental effects differ across medications received, treatment versus control. Consequently, the average cross-arm health difference becomes a biased estimator. Constructively, we show: bias can be altered through choice of control; higher-efficacy controls mitigate upward bias; and efficacy states can be revealed through controls of intermediate efficacy or controls that mimic a subset of efficacy states. Consistent with experimental evidence, our theory implies outcomes within-arm and cross-arm differences can be non-monotone in treatment probability. Finally, we develop novel differences-in-differences and triangle equality tests to detect RCT bias. (C) 2019 Elsevier Inc. All rights reserved.