A placebo is a comparison made to look like the real intervention without its active part, such as a sugar pill. A sham does the same for a procedure: a device that switches on but delivers nothing that matters, or a session that looks complete but leaves out the step being tested. Comparing against a placebo or sham helps separate what an intervention itself does from what expectation, attention, and the passing of time do.
How large the placebo effect really is has been argued for decades. A 1955 paper reported that 35 percent of 1,082 patients across 15 trials were satisfactorily relieved by placebo alone (Beecher, 1955), but a later reanalysis found that natural recovery, regression to the mean, and other factors explained those improvements (Kienle & Kiene, 1997). A review of 130 trials comparing placebo with no treatment found no significant effect on objective or yes-or-no outcomes, and small benefits for pain and other self-reported outcomes (Hróbjartsson & Gøtzsche, 2001).
Meaning still matters. Blocking the body’s endorphins raised pain in people who had responded to a placebo after dental surgery (Levine et al., 1978), and placebos given openly, with people told they were placebos, have outperformed no treatment across dozens of trials (Buergler et al., 2023).
How we use it
Calm, attention, and meaning are real parts of an experience, and we name them as such. That is why the Evidence Gradient gives experience its own tier instead of borrowing the language of mechanism.
References
Beecher, H. K. (1955). The powerful placebo. Journal of the American Medical Association, 159(17), 1602–1606. https://doi.org/10.1001/jama.1955.02960340022006
Buergler, S., Sezer, D., Gaab, J., & Locher, C. (2023). The roles of expectation, comparator, administration route, and population in open-label placebo effects: A network meta-analysis. Scientific Reports, 13, Article 11827. https://doi.org/10.1038/s41598-023-39123-4
Hróbjartsson, A., & Gøtzsche, P. C. (2001). Is the placebo powerless? An analysis of clinical trials comparing placebo with no treatment. New England Journal of Medicine, 344(21), 1594–1602. https://doi.org/10.1056/NEJM200105243442106
Kienle, G. S., & Kiene, H. (1997). The powerful placebo effect: Fact or fiction? Journal of Clinical Epidemiology, 50(12), 1311–1318. https://doi.org/10.1016/S0895-4356(97)00203-5
Levine, J. D., Gordon, N. C., & Fields, H. L. (1978). The mechanism of placebo analgesia. The Lancet, 312(8091), 654–657. https://doi.org/10.1016/S0140-6736(78)92762-9