Effects of frequency and scenario information on the evaluation of large-scale risks

Risk judgments may be based on relative frequency information (RFI) about past accidents and/or on cognitive scenario information (CSI) about possible future accidents. A preceding study revealed that CSI dominates RFI when subjects assess the riskiness (accident probability) of small-scale, personally controllable activities. Our current hypothesis is that RFI is more important when risk judgments concern large-scale, personally less controllable activities. Ninety-six subjects read 16 descriptions of decision problems involving large-scale risks, offering a choice between a risky and a safe alternative. A paragraph containing both RFI and CSI was inserted into each description. Within subjects, RFI varied in the height of the reported accident frequency and in its statistical quality; CSI varied in the number of suggested accident scenarios and in their concreteness. Between two groups of subjects, the suggested personal controllability of the risky activities differed. It was found that subjects base their risk judgments and risky decisions on both types of risk information but that RFI plays a more prominent role when the risks concern large-scale, uncontrollable activities. Earlier findings on specific frequency and scenario information effects were replicated. Personality differences in “locus of control” were found relevant.