  Understanding how people form and revise their perception of risk is central
to designing efficient risk communication methods, eliciting risk awareness,
and avoiding unnecessary anxiety among the public. However, public responses to
hazardous events such as climate change, contagious outbreaks, and terrorist
threats are complex and difficult-to-anticipate phenomena. Although many
psychological factors influencing risk perception have been identified in the
past, it remains unclear how perceptions of risk change when propagated from
one person to another and what impact the repeated social transmission of
perceived risk has at the population scale. Here, we study the social dynamics
of risk perception by analyzing how messages detailing the benefits and harms
of a controversial antibacterial agent undergo change when passed from one
person to the next in 10-subject experimental diffusion chains. Our analyses
show that when messages are propagated through the diffusion chains, they tend
to become shorter, gradually inaccurate, and increasingly dissimilar between
chains. In contrast, the perception of risk is propagated with higher fidelity
due to participants manipulating messages to fit their preconceptions, thereby
influencing the judgments of subsequent participants. Computer simulations
implementing this simple influence mechanism show that small judgment biases
tend to become more extreme, even when the injected message contradicts
preconceived risk judgments. Our results provide quantitative insights into the
social amplification of risk perception, and can help policy makers better
anticipate and manage the public response to emerging threats.
