Causal diagrams, the placebo effect, and the expectation effect

Eyal Shahar, Doron J. Shahar

Research output: Contribution to journalArticle

4 Scopus citations


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.



  • Causal diagrams
  • Effect modification
  • Expectation
  • Placebo

ASJC Scopus subject areas

  • Medicine(all)

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