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Causal diagrams, the placebo effect, and the expectation effect

Authors Shahar E, Shahar DJ

Received 30 July 2013

Accepted for publication 26 August 2013

Published 27 September 2013 Volume 2013:6 Pages 821—828

DOI https://doi.org/10.2147/IJGM.S52209

Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 3


Eyal Shahar,1 Doron J Shahar2

1Division of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, 2Department of Mathematics, College of Science, University of Arizona, Tucson, AZ, USA

Abstract: Using causal diagrams, a formal research methodology, we analyzed several definitions of placebo and the placebo effect. We conclude that placebo is an ambiguous, redundant term and that the so-called placebo effect conceals far more interesting effects that are attributed to the patient's expectation. Biomedical research will benefit from abandoning the term placebo effect and focusing instead on a deeper understanding of the expectation variable, including its causes, effects, and effect modifiers. This avenue of research should be pursued by observational cohorts that are nested within clinical trials.

Keywords: causal diagrams, effect modification, placebo, expectation

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