Incomplete Information, Inferences, and Individual Differences: The Case of Environmental Judgments

A model for inference of missing information is explicated and tested in two studies (Ns = 74, 76) of judgments about two environmental issues (endangered species reintroduction and the siting of a waste processing facility). Participants made judgments of scenarios in which information relevant to the judgment was varied orthogonally and, in some cases, relevant information was missing. The results showed individual differences-as well as intraindividual differences-in the assumptions participants made about missing information and in the tendency to infer missing cues. Reported assumptions about missing information predicted some aspects of the judgments. The data for only a small minority (15%) of the participants were consistent with the inferred values model. Participants may use different methods for dealing with missing information at different times or may not generally follow either an inference or averaging model in such contexts. Less favorable judgments were given for scenarios with incomplete information (the "penalty" effect), and this effect showed individual and intraindividual variation that was related to reported assumptions about missing information. We discuss the implications of these results for societal conflicts over controversial issues and for understanding the sources of individual differences in judgments. Copyright 2000 Academic Press.