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Causal diagrams, the placebo effect, and the expectation effect
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 anonymous peer review
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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