The Effects of “Time” and “Probability” Formats on Risk Perception and Decision‐Making About Long‐Term Hazards

ABSTRACT For long‐term hazards, the likelihood of a hazardous event can be communicated in the format of the probability of occurrence per unit time (probability‐based, e.g., a flood with a 1% chance of occurring annually) or the average time of risk occurrence (time‐based, e.g., a 100‐year flood). This study investigates how the two presentation formats influence risk perception and related behavior in long‐term hazard scenarios, such as typhoons, healthcare, high‐risk occupations, and investments, and further examines the moderating role of probability magnitude. First, we demonstrated that at an extremely low probability level, time‐based formats reduced perceived risk and protective tendency compared to probability‐based formats (Studies 1 and 2). However, as probability increased to a moderately low level, this effect diminished and then reversed, such that time‐based formats increased risk perception and protective tendency compared to probability‐based formats (Study 2). The difference between the two formats diminished again when probabilities reached the moderate‐to‐high range and moved toward 50% (Studies 1 and 2). Second, we revealed that presentation formats also influenced perceived risk differences between options (Study 3) and altered individuals' risk preference between options (Studies 3, 4a, and 4b), with these effects also moderated by probability magnitude. For lower probability events, time‐based formats amplified perceived risk differences between options, promoting preferences for options with lower loss‐probabilities, whereas for higher probability events, this effect weakened and eventually reversed. The findings contribute to related theory by identifying probability magnitude as a key boundary condition under which time‐based and probability‐based formats have different influences on risk perception and behavior. Practically, the results offer implications for risk communication in long‐term hazard contexts, indicating how to choose between time‐based and probability‐based formats according to the size of the probability and the intended persuasive purpose.