with different sensitivities to a chemical or show the consequences of different regulatory decisions on human health benefits. In reality, however, most of the problems that EPA faces have many sources of uncertainty and many intermediate outputs which may covary. For example, the consideration of a number of different health endpoints might influence a decision, or there might be estimates for a number of costs and benefits of a rule, each of which has uncertainty associated with it. Tornado diagrams provide “a pictorial representation of the contribution of each input variable to the output of the decision making model” (Daradkeh et al., 2010).
One line of risk perception research that is relevant to EPA’s communication of uncertainty is the study of the effects that alternative ways of framing risk information have on risk perception and decision making. Experts have been found to be just as susceptible to framing effects as isthe general population (Slovic et al., 1982). Different ways of framing probabilistic information can leave people with different impressions about a risk estimate and, consequently, the confidence in that estimate. For example, stating that “10 percent of bladder cancer deaths in the population can be attributed to arsenic in the water supply” may leave a different impression than stating that “90 percent of bladder cancer deaths in the population can be attributed to factors other than arsenic in the water supply,” even though both statements contain the same information. Choices based on presentations of a range of uncertainty will be similarly influenced by the way that information is presented. Risk estimates that include a wide range of uncertainties may imply that an adverse outcome is possible, even if the likelihood of the adverse outcome occurring is extremely small (NRC, 1989).
Determining the best approach to communicate the uncertainty in a decision needs to be made on a case-by-case basis (Fagerlin et al., 2007; Lipkus, 2007; Nelson et al., 2009; Spiegelhalter et al., 2011; Visschers et al., 2009). There are, however, a number of considerations that should be taken into account when making that decision. The committee discusses the following considerations below: (1) the stage of the decision-making process and the purpose of the communication; (2) the decision context; (3) the type and source of the uncertainty and the whether the uncertainty analysis is qualitative or quantitative; and (4) the audience with which EPA