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Recollection bias is a phenomenon whereby people, after observing 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 explores the phenomenon of recollection bias with respect 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 risks of a future terrorist attack by either an airplane or in a public setting are no higher than they believed respectively before the 9/11 attack and the Boston Marathon bombing. Only one-fifth of respondents are free of any type of recollection bias. Recollection bias with respect to both events is negatively correlated with absolute levels of risk belief. Recollection bias — basically the belief that perceived risks have not increased — also dampens support for a variety of anti-terrorism measures, controlling for the level of risk beliefs and demographic factors. Please note this paper has been updated and replaced by RWP16_003.


Viscusi, W. Kip, and Richard Zeckhauser. "Recollection Bias and Its Underpinnings: Lessons from Terrorism-Risk Assessments." HKS Faculty Research Working Paper Series RWP15-066, October 2015.