Risk perception is the subjective judgement that people make about the characteristics and severity of a risk. Risk perceptions are different for the real risks since they are affected by a wide range of affective (emotions, feelings, moods, etc.), cognitive (gravity of events, media coverage, risk-mitigating measures, etc.), contextual (framing of risk information, availability of alternative information sources, etc.), and individual (personality traits, previous experience, age, etc.) factors. Several theories have been proposed to explain why different people make different estimates of the dangerousness of risks. Three major families of theory have been developed: psychology approaches (heuristics and cognitive), anthropology/sociology approaches (cultural theory) and interdisciplinary approaches (social amplification of risk framework). Early theories The study of risk perception arose out of the observation that experts and lay people often disagreed about how risky various technologies and natural hazards were. The mid 1960s saw the rapid rise of nuclear technologies and the promise of clean and safe energy. However, public perception shifted against this new technology. Fears of both longitudinal dangers to the environment and immediate disasters creating radioactive wastelands turned the public against this new technology. The scientific and governmental communities asked why public perception was against the use of nuclear energy when all the scientific experts were declaring how safe it really was. The problem, as non-experts perceived it, was a difference between scientific facts and an exaggerated public perception of the dangers. A key early paper was written in 1969 by Chauncey Starr. Starr used a revealed preference approach to find out what risks are considered acceptable by society. He assumed that society had reached equilibrium in its judgment of risks, so whatever risk levels actually existed in society were acceptable. His major finding was that people will accept risks 1,000 times greater if they are voluntary (e.g. driving a car) than if they are involuntary (e.g. a nuclear disaster). This early approach assumed that individuals behave rationally by weighing information before making a decision, and that individuals have exaggerated fears due to inadequate or incorrect information. Implied in this assumption is that additional information can help people understand true risk and hence lessen their opinion of danger. While researchers in the engineering school did pioneer research in risk perception, by adapting theories from economics, it has little use in a practical setting. Numerous studies have rejected the belief that additional information alone will shift perceptions. Psychological approach