BACKGROUND Choice has been found to facilitate placebo effects for single-session treatments where standard placebo treatment without choice failed to elicit a placebo effect. However, it is unknown whether choice can enhance the placebo effect for treatments occurring over a period of days and where placebo effects are readily established without choice. PURPOSE We tested whether single or daily choice between two (placebo) treatments enhanced the placebo effect for sleep difficulty relative to no choice and no treatment over a 1 week period. METHODS One-hundred and seventeen volunteers self-identifying with sleep difficulty were recruited under the guise of a hypnotic trial and randomized to one of the four groups. Self-reported outcomes included insomnia severity, fatigue, total sleep time (TST), sleep onset latency (SOL), perceived sleep quality (PSQ), and treatment satisfaction. Objective TST and SOL were assessed in a subsample via actigraphy. RESULTS Overall, placebo treatment significantly improved insomnia severity, fatigue, and PSQ, confirming a placebo effect on these outcomes. However, both traditional and Bayesian analysis indicated no benefit of choice on the placebo effect on any sleep outcome. Mediation analysis of the overall placebo effect indicated that expectancy completely mediated the placebo effects for insomnia severity and PSQ and partially mediated the placebo effect for fatigue. CONCLUSION These findings suggest that choice does not enhance the placebo effect over longer treatment periods (up to 7 days) when placebo effects are readily established without choice. As such, any benefit of choice on placebo effects may be confined to quite specific circumstances. CLINICAL TRIALS REGISTRATION ACTRN12618001199202.

中文翻译：

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选择，期望和安慰剂对睡眠困难的影响。

背景技术已经发现选择对于单阶段治疗有利于安慰剂作用，其中未经选择的标准安慰剂治疗不能引起安慰剂作用。然而，对于几天内发生的治疗，选择是否可以增强安慰剂作用尚不清楚，并且无需选择就可以轻易确立安慰剂作用。目的我们测试了两种（安慰剂）治疗之间的单日选择或每日选择是否相对于1周内无选择和无治疗相对于睡眠困难增强了安慰剂效果。方法以催眠试验的名义招募一百一十七名自我识别为睡眠困难的志愿者，并随机分为四组之一。自我报告的结局包括失眠严重程度，疲劳，总睡眠时间（TST），睡眠发作潜伏期（SOL），觉察到的睡眠质量（PSQ）和治疗满意度。客观TST和SOL是通过书法记录在一个子样本中进行评估的。结果总的来说，安慰剂治疗可显着改善失眠严重程度，疲劳和PSQ，从而证实了安慰剂对这些结局的影响。然而，传统和贝叶斯分析均表明选择安慰剂对任何睡眠结局均无益处。总体安慰剂作用的中介分析表明，期望值完全调节了失眠严重程度和PSQ的安慰剂作用，部分地调节了疲劳的安慰剂作用。结论这些发现表明，在没有选择的情况下就可以很容易地建立起安慰剂作用，选择不会在更长的治疗期间（长达7天）内增强安慰剂作用。因此，选择安慰剂效果的任何益处都可能仅限于非常具体的情况。临床试验注册法12618001199202。