The Psychophysics of Terror Attack Casualty Counts

In communicating the risk that terror attacks pose to the public, government agencies and other organizations must understand which characteristics of an attack contribute to the public's perception of its severity. An attack's casualty count is one of the most commonly used metrics of a terror attack's severity, yet it is unclear whether the public responds to information about casualty count when forming affective and cognitive reactions to terror attacks. This study sought to characterize the “psychophysical function” relating terror attack casualty counts to the severity of the affective and cognitive reactions they elicit. We recruited n = 684 Mechanical Turk participants to read a realistic vignette depicting either a biological or radiological terror attack, whose death toll ranged from 20 to 50,000, and rated their levels of fear and anger along with the attack's severity. Even when controlling for the perceived plausibility of the scenarios, participants’ severity ratings of each attack were logarithmic with respect to casualty count, while ratings of fear and anger did not significantly depend on casualty count. These results were consistent across attack weapon (biological vs. radiological) and time horizon of the casualties (same-day or anticipated to occur over several years). These results complement past work on life loss valuation and highlight a potential bifurcation between the public's affective and cognitive evaluations of terror attacks.