SUPPORT THEORY

A great deal of psychological research has addressed the nature and quality of people's intuitive judgments of likelihood. Much of this work has sought to characterize the simple mental operations, often termed heuristics, that govern people's assessments of probabilities and frequencies. The heuristics initially identified by Daniel Kahneman and Amos Tversky – availability, representativeness, and anchoring, among others – describe and explain many phenomena in judgment under uncertainty. These heuristics have been particularly helpful in identifying conditions under which people closely conform to, or radically deviate from, the requirements of probability theory.

Support theory, a formal descriptive account of subjective probability introduced by Tversky and Koehler (1994), offers the opportunity to weave together the different heuristics into a unified account. The theory can accommodate many mechanisms (such as the various heuristics) that influence subjective probability, but integrates them via the construct of support. Consequently, support theory can account for numerous existing empirical patterns in the literature on judgment under uncertainty.

The original works describing the major heuristics underlying likelihood judgments are presented in Kahneman, Slovic, and Tversky (1982). Previous chapters of this book contain selections from the initial statements of support theory that invoke several heuristics to account for various properties of support. Our goal in this chapter is twofold: to summarize recent developments in support theory, and to suggest some possible directions for future research.