This theoretical paper aims to unravel the psychological mechanisms explaining how terrorism threat alerts can lead to public underestimation of the risk of a terrorist attack. We discuss, compare and critique a large variety of literature from psychology, public administration, and communication science. We found that throughout the world, people find threat alerts confusing. We provide an extensive psychological explanation of how confusion can lead to optimism bias and, ultimately, to underestimating terrorism threats. Literature suggests implementing three design elements to reduce the confusion that current (leveled) threat alerts create: keep it simple, call for action, and make international agreements for standardization. We discuss these practical design suggestions and give detailed directions for future research to assess the impact of terrorism threat alerts empirically.

In democratic societies, governments cannot act in isolation from public opinion. This is especially true regarding terrorism, where public perception is the instrument targeted by terrorists to achieve their political goals. Nevertheless, governments must also be able to resist public pressure and preserve individual rights. All this suggests that researching public perception of terrorist attacks is crucial. We make an important contribution in this direction by measuring the importance the public assigns to various attributes of terrorist attacks. Using novel methodology (conjoint experiment) and survey data from the UK and The Netherlands (N = 6,315), we find that people are concerned with attacks by immigrants (in the Netherlands), and by individuals acting as part of a terror cell, and with jihadist motivation. Furthermore, past experience with specific terrorist tactics drive preference to address such attacks more than others. In both countries people strongly focus on the severity of attacks, and under-weigh probabilities. The terror attack in the Netherlands in 2019 provided an opportunity to examine perception right after an actual attack. Also there we have found that people’s concerns are driven by experience with specific attacks. A better understanding of terrorism perception can inform policymakers about the gap between optimal strategies to combat terrorism and the expectations of the public.