Why do we believe misinformation more easily when it’s repeated many times?

The Illusory Truth Effect

, explained.
Bias

What is the Illusory Truth Effect?

The illusory truth effect, also known as the illusion of truth, describes how when we hear the same false information repeated again and again, we often come to believe it is true. Troublingly, this even happens when people should know better—that is, when people initially know that the misinformation is false.

The image shows a line graph labeled "Illusory Truth Effect," where the perceived truth of a lie increases with the number of times it's heard, as depicted by an upward-sloping line.

Where this bias occurs

Imagine there’s been a cold going around your office lately and you really want to avoid getting sick. Over the years, you’ve heard a lot of people say that taking vitamin C can help prevent sickness, so you stock up on some tasty orange-flavored vitamin C gummies.

You later find out that there’s no evidence vitamin C prevents colds (though it might make your colds go away sooner!).18 However, you decide to keep taking the gummies anyways, feeling like they still might have some preventative ability. This is an example of the illusory truth effect, since your repeated exposure to the myth created the gut instinct that it was true.

Related Biases

Sources

  1. Kahneman, D. (2011). Thinking, fast and slow. Macmillan.
  2. Zajonc, R. B., & Rajecki, D. W. (1969). Exposure and affect: A field experiment. Psychonomic Science, 17(4), 216-217.
  3. Fazio, L. K., Brashier, N. M., Payne, B. K., & Marsh, E. J. (2015). Knowledge does not protect against illusory truth. Journal of Experimental Psychology: General, 144(5), 993-1002. https://doi.org/10.1037/xge0000098
  4. Vosoughi, S., Roy, D., & Aral, S. (2018). The spread of true and false news online. Science, 359(6380), 1146-1151. https://doi.org/10.1126/science.aap9559
  5. Meyer, R. (2018, March 8). The grim conclusions of the largest-ever study of fake news. The Atlantic. https://www.theatlantic.com/technology/archive/2018/03/largest-study-ever-fake-news-mit-twitter/555104/
  6. Samuels, E. (2020, February 21). How misinformation on WhatsApp led to a mob killing in India. The Washington Post. https://www.washingtonpost.com/politics/2020/02/21/how-misinformation-whatsapp-led-deathly-mob-lynching-india/
  7. Anderson, J., & Rainie, L. (2020, August 17). The future of truth and misinformation online. Pew Research Center: Internet, Science & Tech. https://www.pewresearch.org/internet/2017/10/19/the-future-of-truth-and-misinformation-online/
  8. Dreyfuss, E. (2017, February 11). Want to make a lie seem true? Say it again. And again. And again. WIRED. https://www.wired.com/2017/02/dont-believe-lies-just-people-repeat/
  9. Montpetit, J., & MacFarlane, J. (2020, September 12). Latest anti-mask protest in Montreal draws large crowds who say threat of COVID-19 overstated. CBC News. https://www.cbc.ca/news/canada/montreal/anti-mask-protest-montreal-1.5722033
  10. Warren, M. (2019, June 26). Higher intelligence and an analytical thinking style offer no protection against “The illusory truth effect” – Our tendency to believe repeated claims are true. Research Digest. https://digest.bps.org.uk/2019/06/26/higher-intelligence-and-an-analytical-thinking-style-offer-no-protection-against-the-illusory-truth-effect-our-tendency-to-believe-repeated-claims-are-more-likely-to-be-true/
  11. Warren, M. (2020, April 16). When false claims are repeated, we start to believe they are true — Here’s how behaving like a fact-checker can help. Research Digest. https://digest.bps.org.uk/2019/09/12/when-false-claims-are-repeated-we-start-to-believe-they-are-true-heres-how-behaving-like-a-fact-checker-can-help/
  12. Fleming, N. (2020, June 17). Coronavirus misinformation, and how scientists can help to fight it. Nature. https://www.nature.com/articles/d41586-020-01834-3
  13. Hasher, L., Goldstein, D., & Toppino, T. (1977). Frequency and the Conference of Referential Validity. Journal of Verbal Learning and Verbal Behavior, 16, 107-112. http://bear.warrington.ufl.edu/brenner/mar7588/Papers/hasher-et-al-jvvb-1977.pdf
  14. Pennycook, G., Cannon, T. D., & Rand, D. G. (2018). Prior exposure increases perceived accuracy of fake news. Journal of Experimental Psychology: General, 147(12), 1865–1880. https://doi.org/10.1037/xge0000465
  15. White, C. M., & Hernandez, A. V. (2020). Why your Patients’ Believing Hydroxychloroquine and Chloroquine are 90% Effective for COVID‐19 is 100% Dangerous. The Journal of Clinical Pharmacology.
  16. McGinley, L. (2020, July 16). Hydroxychloroquine studies show drug is not effective for early treatment of mild covid-19. The Washington Post. https://www.washingtonpost.com/health/2020/07/16/hydroxychloroquine-studies-show-drug-is-not-effective-early-treatment-mild-covid-19/
  17. Caulfield, T. (2020, April 19). How coronavirus is reinforcing the real-life risks of celebrity woo. NBC News. https://www.nbcnews.com/think/opinion/dr-oz-s-hydroxychloroquine-advocacy-seduces-trump-coronavirus-wellness-woo-ncna1185596
  18. Douglas, R., Chalker, E., & Treacy, B. (1998). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. https://doi.org/10.1002/14651858.cd000980
  19. Krockow, E. (2018, September 27). How many decisions do we make each day? Psychology Today. https://www.psychologytoday.com/ca/blog/stretching-theory/201809/how-many-decisions-do-we-make-each-day

About the Authors

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Dan Pilat

Dan is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. Dan has a background in organizational decision making, with a BComm in Decision & Information Systems from McGill University. He has worked on enterprise-level behavioral architecture at TD Securities and BMO Capital Markets, where he advised management on the implementation of systems processing billions of dollars per week. Driven by an appetite for the latest in technology, Dan created a course on business intelligence and lectured at McGill University, and has applied behavioral science to topics such as augmented and virtual reality.

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Dr. Sekoul Krastev

Sekoul is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. A decision scientist with a PhD in Decision Neuroscience from McGill University, Sekoul's work has been featured in peer-reviewed journals and has been presented at conferences around the world. Sekoul previously advised management on innovation and engagement strategy at The Boston Consulting Group as well as on online media strategy at Google. He has a deep interest in the applications of behavioral science to new technology and has published on these topics in places such as the Huffington Post and Strategy & Business.

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