The placebo effect, used today as the benchmark to evaluate treatment efficacy, plays a major functional role in traditional medical practices. To better understand its effect at the population level, I use a formal approach to examine the population dynamics of the placebo effect and show a reciprocal causal relationship between belief and efficacy: belief in the efficacy of treatments enhances their realized efficacy, which in turn increases people’s confidence in their therapeutic power. A unique equilibrium for subjective belief and realized efficacy always exists. Its magnitude depends on how beliefs are constructed (relative weight on observed action vs. observed outcome). I further investigate how the placebo effect affects the maintenance of existing medical technologies and the invasion of new technologies by explicitly modeling a belief construction process. Analytical and simulation results show that although the placebo effect primarily suppresses the spread of new technologies, it may occasionally enhance the adoption of superior technological variants under specific parameter combinations.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Price excludes VAT (USA)
Tax calculation will be finalised during checkout.
Availability of Data and Material
Code used for simulation is available at https://github.com/kevintoy/placebo_effect
On the other hand, people may become skeptical of the treatment if it doesn’t yield positive results (Bianchi 1989).
Annus, A. (2010). Divination and Interpretation of Signs in the Ancient World. Oriental Institute Seminars.
Aschwanden, H., & Cooper, U. (1987). Symbols of death: an analysis of the consciousness of the Karanga. In Shona heritage series (p. 389). Gweru, Zimbabwe: Mambo Press. https://ehrafworldcultures.yale.edu/document?id=fs05-021
Bianchi, C. C. (1989). Gubida illness and religious ritual among the Garifuna of Santa Fe, Honduras: an ethnopsychiatric analysis. Ann Arbor, Mich.: University Microfilms International. https://ehrafworldcultures.yale.edu/document?id=sa12-016
Boyd, R., Richerson, P., & Henrich, J. (2013). The cultural evolution of technology: Facts and theories. In P. J. Richerson and M. H. Christiansen (Ed.), Cultural Evolution: Society, Language, and Religion. MIT Press. http://www2.psych.ubc.ca/~henrich/pdfs/Boyd Richerson Henrich The cultural evolution of technology 7.pdf. Accessed 26 March 2019
Boyd, R., & Richerson, P. J. (1985). Culture and the evolutionary process. University of Chicago Press.
Culwick, A. T. (Arthur T., Culwick G. M., M., & Kiwanga, T. (1935). Ubena of the Rivers. London: G. Allen & Unwin, Ltd. https://ehrafworldcultures.yale.edu/document?id=fn31-001
Day, T., & Bonduriansky, R. (2011). A Unified Approach to the Evolutionary Consequences of Genetic and Nongenetic Inheritance. The American Naturalist. https://doi.org/10.1086/660911
De Craen, A. J. M., Kaptchuk, T. J., Tijssen, J. G. P., & Kleijnen, J. (1999). Placebos and placebo effects in medicine: Historical overview. Journal of the Royal Society of Medicine. https://doi.org/10.1177/014107689909201005
De Craen, A. J. M., Tijssen, J. G. P., De Gans, J., & Kleijnen, J. (2000). Placebo effect in the acute treatment of migraine: Subcutaneous placebos are better than oral placebos. Journal of Neurology. https://doi.org/10.1007/s004150050560
Evans-Pritchard, E. (1937). Witchcraft, oracles and magic among the Azande. Clarendon Press.
Faasse, K., & Petrie, K. J. (2016). From Me to You: The Effect of Social Modeling on Treatment Outcomes. Current Directions in Psychological Science. https://doi.org/10.1177/0963721416657316
Giraldeau, L. A., & Lefebvre, L. (1987). Scrounging prevents cultural transmission of food-finding behaviour in pigeons. Animal Behaviour. https://doi.org/10.1016/S0003-3472(87)80262-2
Hammami, M. M., Al-Gaai, E. A., Alvi, S., & Hammami, M. B. (2010). Interaction between drug and placebo effects: A cross-over balanced placebo design trial. Trials. https://doi.org/10.1186/1745-6215-11-110
Harrell, S. (1983). Belief and unbelief in a Taiwan village. Ann Arbor, Mich.: Xerox University Microfilms. https://ehrafworldcultures.yale.edu/document?id=ad05-011
Henrich, J., & Boyd, R. (1998). The Evolution of Conformist Transmission and the Emergence of Between-Group Differences. Evolution and Human Behavior. https://doi.org/10.1016/S1090-5138(98)00018-X
Henrich, J., & Gil-White, F. J. (2001). The evolution of prestige: Freely conferred deference as a mechanism for enhancing the benefits of cultural transmission. Evolution and Human Behavior. https://doi.org/10.1016/S1090-5138(00)00071-4
Henrich, J., & McElreath, R. (2003). The Evolution of Cultural Evolution. Evolutionary Anthropology. https://doi.org/10.1002/evan.10110
Heyes, C. M. (1994). Social learning in animals: Categories and mechanisms. Biological Reviews of the Cambridge Philosophical Society. https://doi.org/10.1111/j.1469-185X.1994.tb01506.x
Hong, Z. (2016). Combining Conformist and Payoff Bias in Cultural Evolution: An Integrated Model for Human Decision Making. Under review.
Hong, Z. & Henrich, J. (2021). The cultural evolution of epistemic practices: the case of divination. Human Nature (forthcoming).
Horton, R. (1967). African Traditional Thought and Western Science. Africa. https://doi.org/10.2307/1158253
Hróbjartsson, A., & Gøtzsche, P. C. (2010). Placebo interventions for all clinical conditions. Cochrane Database of Systematic Reviews. https://doi.org/10.1002/14651858.CD003974.pub3
Humphrey, N. (2002). Great expectations: the evolutionary psychology of faith- healing and the placebo effect. In The mind made flesh.
Humphrey, N. (2018). Shamans as healers: When magical structure becomes practical function. The Behavioral and Brain Sciences. https://doi.org/10.1017/S0140525X17002084
Hunsley, J., & Westmacott, R. (2007). Interpreting the magnitude of the placebo effect: Mountain or molehill? Journal of Clinical Psychology. https://doi.org/10.1002/jclp.20352
Hunter, P. (2007). A question of faith. Exploiting the placebo effect depends on both the susceptibility of the patient to suggestion and the ability of the doctor to instil trust. EMBO Reports. https://doi.org/10.1038/sj.embor.7400905
Kaptchuk, T. J. (1998). Intentional Ignorance: A History of Blind Assessment and Placebo Controls in Medicine. Bulletin of the History of Medicine. https://doi.org/10.1353/bhm.1998.0159
Kaptchuk, T. J., Goldman, P., Stone, D. A., & Stason, W. B. (2000). Do medical devices have enhanced placebo effects? Journal of Clinical Epidemiology. https://doi.org/10.1016/S0895-4356(00)00206-7
Kaptchuk, T. J., & Miller, F. G. (2015). Placebo effects in medicine. New England Journal of Medicine. https://doi.org/10.1056/NEJMp1504023
Kirmayer, L. J. (1994). Improvisation and authority in illness meaning. Culture, Medicine and Psychiatry. https://doi.org/10.1007/BF01379449
Laland, K. N. (2004). Social learning strategies. Learning and Behavior. https://doi.org/10.3758/bf03196002
Lancy, D. F., Bock, J., & Gaskins, S. (2010). The anthropology of learning in childhood. Rowman Altamira.
Misra, S. (2012). Randomized double blind placebo control studies, the “gold Standard” in intervention based studies. Indian Journal of Sexually Transmitted Diseases. https://doi.org/10.4103/0253-7184.102130
Miton, H., Claidière, N., & Mercier, H. (2015). Universal cognitive mechanisms explain the cultural success of bloodletting. Evolution and Human Behavior. https://doi.org/10.1016/j.evolhumbehav.2015.01.003
Murdock, G. P. (1980). Theories of Illness a World Survey. University of Pittsburgh Press. https://philpapers.org/rec/MURTOI. Accessed 28 March 2019
Perreault, C., Moya, C., & Boyd, R. (2012). A Bayesian approach to the evolution of social learning. Evolution and Human Behavior. https://doi.org/10.1016/j.evolhumbehav.2011.12.007
Plotkin, H. C. (1988). The role of behavior in evolution. MIT press.
Shapiro, A. K. (1969). Iatroplacebogenics. International Pharmacopsychiatry. https://doi.org/10.1159/000468855
Sigerist, H. E. (Henry E. (1951). A history of medicine. Oxford University Press. https://global.oup.com/academic/product/a-history-of-medicine-9780195050790?cc=us&lang=en&. Accessed 30 March 2019
Smith, E. W., & Dale Andrew Murray, d. 1919. (1920). Ila-speaking peoples of Northern Rhodesia: vol. 1. London: MacMillan and Co. https://ehrafworldcultures.yale.edu/document?id=fq06-001
Trimmer, P. C., Marshall, J. A. R., Fromhage, L., McNamara, J. M., & Houston, A. I. (2013). Understanding the placebo effect from an evolutionary perspective. Evolution and Human Behavior. https://doi.org/10.1016/j.evolhumbehav.2012.07.004
Turnbull, C. M. (1965). Wayward servants: the two worlds of the African Pygmies. Garden City, N.Y.: The Natural History Press. https://ehrafworldcultures.yale.edu/document?id=fo04-002
Tylor, E. B. (1871). Primitive culture: researches into the development of mythology, philosophy, religion, art, and custom (Vol. 2). J. Murray.
Vale, G. L., Flynn, E. G., Kendal, J., Rawlings, B., Hopper, L. M., Schapiro, S. J., et al. (2017). Testing differential use of payoff-biased social learning strategies in children and chimpanzees. Proceedings of the Royal Society b: Biological Sciences. https://doi.org/10.1098/rspb.2017.1751
Vickers, A. J., Vertosick, E. A., Lewith, G., MacPherson, H., Foster, N. E., Sherman, K. J., et al. (2018). Acupuncture for Chronic Pain: Update of an Individual Patient Data Meta-Analysis. Journal of Pain. https://doi.org/10.1016/j.jpain.2017.11.005
Waber, R. L., Shiv, B., Carmon, Z., & Ariely, D. (2008). Commercial features of placebo and therapeutic efficacy. JAMA - Journal of the American Medical Association. https://doi.org/10.1001/jama.299.9.1016
Wartolowska, K. A., Feakins, B. G., Collins, G. S., Cook, J., Judge, A., Rombach, I., et al. (2016). The magnitude and temporal changes of response in the placebo arm of surgical randomized controlled trials: A systematic review and meta-analysis. Trials, 17(1), 589.
Wood, L. A., Kendal, R. L., & Flynn, E. G. (2013). Whom do children copy? Model-based biases in social learning. Developmental Review. https://doi.org/10.1016/j.dr.2013.08.002
I thank Dr. Joseph Henrich for his helpful suggestions and feedback in developing this project, Graham Noblit for providing constructive comments for an earlier version of the paper, and Mona Xue for carefully proofreading the final version of the manuscript.
Conflicts of Interest
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
“What he believes he therefore sees; and what he sees he therefore believes.”
About this article
Cite this article
Hong, Z. The Population Dynamics of the Placebo Effect and Its Role in the Evolution of Medical Technology. Hum Ecol 50, 11–22 (2022). https://doi.org/10.1007/s10745-021-00271-8