plans to decrease those uncertainties. Regardless of the audience, however, EPA should use its communication opportunities to provide audiences with information as well as to gather information from the audience that could help either decrease acknowledged uncertainties or identify additional uncertainties that might affect the decision.

Another potential option now that many documents are available electronically through the Internet is to use layered hypertext for more complex uncertainty analysis. That is, the main body of text and the summary sections of EPA’s decision document could contain a summary of the uncertainty analyses conducted and could also include a link to appendixes or other documents that present full details of the analyses. That would provide summary information for all audiences as well as further details of the uncertainty analyses for technical audiences or others with an interest in seeing all the details.


Uncertainty information concerning probabilities has been found to be susceptible to biases by both experts and non-experts (Hoffrage et al., 2000; Kloprogge et al., 2007; Slovic, 2000; Slovic et al., 1979, 1981; Tversky and Kahneman, 1974). When people’s judgments about a risk are biased, risk management and communication efforts may not be as effective as they would otherwise be. Biases can stem from the characteristics of an individual or group or can be embedded in the framing of a message; both types can influence the interpretation of a message. Communicators of information about uncertainty cannot completely eliminate these biases, but they should be aware of the potential for biases to influence the acceptance of and reaction to probabilistic information and, to the extent possible, account for these biases by adjusting communication efforts. These types of biases are discussed below.

Personal Biases One bias that can affect how people interpret probabilistic information is termed availability bias. People tend to judge events that are easily recalled as more risky or more likely to occur than events that are not readily available to memory (see Kloprogge et al., 2007; Slovic et al., 1979; Tversky and Kahneman, 1974). An event may have more availability if it occurred recently, if it was a high-profile event, or if it has some other significance for an individual or group. The overestimation of rare causes of death that have been sensationalized by the media is an example of availability bias. One implication of availability bias that communicators of risk and uncertainty information should be aware of is that the discussion of a risk may increase its perceived riskiness, regardless of what the actual risk may be (Kloprogge et al., 2007). For example, evidence indicates that

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