The examples on AIDS and on drunk driving accidents given in the last slide are consistent with the risk perception summarized in the chart here, which was adapted from the works of Faustman and Omenn (1996), Morgan (1993), and Slovic (1988). Like AIDS, diseases caused by cigarette smoking are both observable and controllable. Yet there are more cigarette smokers today than should be. Pesticides, nuclear weapons fallout, radioactive waste are among those listed under the uncontrollable as well as not observable group. Risks represented by this rightmost bar are perceived as high or great, primarily because they are unknown to science and the exposures involved are uncontrollable or involuntary. As pointed out by Faustman and Omenn, this group of risks is more likely to provoke calls for government regulation.

The above risk perception rests upon two human behavioral factors: Perceived (un)controllability and (un)familiarity with the hazard involved. People tend to accept much higher risks associated with voluntary activities than with those imposed on them without their consent. The shock, fear, and horror to people tend to multiply when the event is unexpected or sudden, or when the extent or nature of the risk is complex.

Insofar as human behavior is involved, individuals normally react differently to most misfortunes or hazardous events, as do groups or organizations. According to Faustman and Omenn, in a study by Neil et al. (1994), toxicologists in the government, industry, and academia were found to respond differently to chemical hazards.