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Recollection bias is the phenomenon whereby people who observe a highly unexpected event hold current risk beliefs about a similar event that are no higher than their recollection of their prior beliefs. This article replicates and extends the authors’ previous study of recollection bias in relation to individuals’ perceptions of the risks of terrorism attacks. Over 60% of respondents in a national U.S. sample of over 900 adults believe that the current risk of a future terrorist attack by either an airplane or in a public setting is no higher than they recall having believed, respectively, before the 9/11 attack and before the Boston Marathon bombing. By contrast, a rational Bayesian model would update to a higher currently assessed risk of these previously uncontemplated events. Recollection bias is a persistent trait: individuals who exhibited this bias for the 9/11 attack exhibited it for the Boston Marathon bombing. Only one-fifth of respondents are free of any type of recollection bias. Recollection bias is negatively correlated with absolute levels of risk belief. Recollection bias in relation to highly unexpected terrorist events—the belief that perceived risks did not increase after the surprise occurrence—dampens support for a variety of anti-terrorism measures, controlling for the level of risk beliefs and demographic factors. Persistent recollection bias for both 9/11 and the Boston Marathon bombing is especially influential in diminishing support for protective policy measures, such as surveillance cameras in public places. Given that public attitudes influence policy, educating the public about risk is critical.


Viscusi, W. Kip, and Richard J. Zeckhauser. "Recollection Bias and Its Underpinnings: Lessons from Terrorism Risk Assessments." Risk Analysis 37.5 (January 2017): 969-981.