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Statistical inference in randomized consent designs in the presence of Hawthorne

Randomized consent designs have been advocated in some setting. It has been argued that the use of the randomized consent designs is justified as it eliminates the so-called Hawthorne effect in the control group. Besides the ethical issue in not informing the patients, there are other potentially serious issues regarding the confounding and resultant bias in treatment comparison. This is particularly so in behavioral intervention trials. There is not only the placebo effect, but also the so-called Hawthorn effect that could muddy the comparisons. Based on a randomized consent design with control and intervention which results in three distinct groups, this presentation will show using very simple statistical contrasts why unbiased comparison is impossible due to confounding and self-selection.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

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Kim, K. Statistical inference in randomized consent designs in the presence of Hawthorne. Trials 16 (Suppl 2), P137 (2015).

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