What are the chances that you will be the victim of a crime on your way home this evening? How likely is it that you will contract cancer from smoking, eating unhealthy foods, or ingesting environmental toxins? Statisticians and scientists have a set of tools to answer these questions-statistics and rationality. What about the rest of us? Most people, when faced with questions like how common, how often, how probable, or how likely, are unable to respond with firm, confident replies. Most people have only an intuitive “feel” when making judgments about probabilities. But they must still make judgments about and choices between alternative risk management strategies or whom to support in public policy debates about health, safety, and the environment.

On what basis do people make such probability judgments? How rational are these judgments? How do such judgments affect how people make choices? Why are people's choices, especially under conditions of risk and uncertainty, seemingly inconsistent? These are the key questions facing scholars who seek to understand judgment and decision making. Researchers working at the intersection of psychology, economics, and the policy sciences have found that people do have a systematic way of arriving at these judgments and choices. But this systematic pattern does not conform to the rational decision process advocated and used by economists and statisticians. Instead, people seem to follow certain heuristics or rules of thumb that often do a reasonably good job of helping people make judgments under conditions of uncertainty and low levels of information.