Judging Cumulative Risk1

The accuracy of young adults' perceptions of how cumulative risks to life, health, and property change over time was tested by asking subjects to judge the long-term probabilities associated with different periods of exposure to risks that are very small in the short term. Process analyses revealed evidence that strategy choice and associated accuracy depended on context and framing variables. Subjects asked to judge conjunctive probabilities adopted a variety of strategies, all of which failed to yield consistently accurate long-term probability judgments. However, subjects asked to judge disjunctive probabilities often reframed the probability questions into questions about the expected number of times the hazard would strike, which they could answer more accurately. Implications of the research for promoting public understanding of the long-term implications of cumulative risks are discussed.