One of the fundamental questions addressed by risk-benefit analysis is "How safe is safe enough?" Chauncey Starr has proposed that economic data be used to reveal patterns of acceptable risk-benefit tradeoffs. The present study investigates an alternative technique, in which psychometric procedures were used to elicit quantitative judgments of perceived risk, acceptable risk, and perceived benefit for each of 30 activities and technologies. The participants were seventy-six members of the League of Women Voters. The results indicated little systematic relationship between perceived existing risks and benefits of the 30 risk items. Current risk levels were generally viewed as unacceptably high. When current risk levels were adjusted to what would be considered acceptable risk levels, however, risk was found to correlate with benefit. Nine descriptive attributes of risk were also studied. These nine attributes seemed to tap two basic dimensions of risk. These dimensions proved to be effective predictors of the tradeoff between acceptable risk and perceived benefit. The limitations of the present study and the relationship between this technique and Starr's technique are discussed, along with the implications of the findings for policy decisions.

People are often overconfident in evaluating the correctness of their knowledge. The present studies investigated the possibility that assessment of confidence is biased by attempts to justify one's chosen answer. These attempts include selectively focusing on evidence supporting the chosen answer and disregarding evidence contradicting it. Experiment 1 presented subjects with two-alternative questions and required them to list reasons for and against each of the alternatives prior to choosing an answer and assessing the probability of its being correct. This procedure produced a marked improvement in the appropriateness of confidence judgments. Experiment 2 simplified the manipulation by asking subjects first to choose an answer and then to list (a) one reason supporting that choice, (b) one reason contradicting it, or (c) one reason supporting and one reason contradicting. Only the listing of contradicting reasons improved the appropriateness of confidence. Correlational analyses of the data of Experiment 1 strongly suggested that the confidence depends on the amount and strength of the evidence supporting the answer chosen. One remarkable characteristic of human memory is its knowledge of its own content, Judgments of confidence in the correctness of recall and recognition performance are

A series of experiments studied how people judge the frequency of death from various causes. The judgments exhibited a highly consistent but systematically biased subjective scale of frequency. Two kinds of bias were identified: (a) a tendency to overestimate small frequencies and underestimate larger ones, and (b) a tendency to exaggerate the frequency of some specific causes and to underestimate the frequency of others, at any given level of objective frequency. These biases were traced to a number of possible sources, including disproportionate exposure, memorability, or imaginability of various events. Subjects were unable to correct for these sources of bias when specifically instructed to avoid them. Comparisons with previous laboratory studies are discussed, along with methods for improving frequency judgments and the implications of the present findings for the management of societal hazards.How well can people estimate the fre-how small a difference in frequency can be quencies of the lethal events they may en-reliably detected? Do people have a concounter in life (e.g., accidents, diseases, sistent internal scale of frequency for such homicides, suicides, etc.) ? More specifically, events? What factors, besides actual frequency, influence people's judgments?The answers to these questions may have to society. Citizens must Defense and was monitored by the Office of Naval assess rlsks accurately in order to mobilize Research under Contracts N00014-76-C-0074 and society's resources effectively for reducing N00074-78-C-0100 (ARPA Order Nos. 3052 and hazards and treating their victims. Official ,5469) under subcontract to Oregon Research In-reco nition of the irn p 0r t a nce of valid risk . , ,.,<<., • ^ » 0722 to Perceptronics, Inc. from Decisions and assessments is found m the vital statistics Designs, Inc. that are carefully tabulated and periodically We would like to thank Nancy Collins and reported to the public (see Figure 1 ). There Peggy Roecker for extraordinary diligence and ; Sj i lowev er, no guarantee that these statispatience in typing and data analysis. We are also .

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How often are people wrong when they are certain that they know the answer to a question ? The studies reported here suggest that the answer is "too often." For a variety of general-knowledge questions (e.g., absinthe is [a] a liqueur or [b] a precious stone), subjects first chose the most likely answer and then indicated their degree of certainty that the answer they had selected was, in fact, correct. Across several different question and response formats, subjects were consistently overconfident. They had sufficient faith in their confidence judgments to be willing to stake money on their validity. The psychological bases for unwarranted certainty are discussed in terms of the inferential processes whereby knowledge is constructed from perceptions and memories.

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