141 © 1996 Psychology Press, an imprint of Erlbaum (UK) Taylor & Francis Ltd THINKING AND REASONING, 1996, 2 (2/3), 141–173 The Methodology of Social Judgement Theory Ray W. Cooksey University of New England, Australia Social Judgement Theory (SJT) evolved from Egon Brunswik’s Probabilistic Functionalist psychology coupled with multiple correlation and regression-based statistical analysis. Through its representational device, the Lens Model, SJT has become a widely used, systems-oriented perspective for analysing human judgement in specific ecological circumstances. Judgements are assumed to result from the integration of different cues or sources of perceptual information from the environment. Special advantages accrue to the SJT approach when criterion values (or correct values) for judgement are also available, as this permits the comparison of judgement processes to environmental processes and leads naturally to the generation of cognitive feedback as an aid to facilitate learning. In contrast to more prescriptive approaches to decision analysis, the SJT approach analyses judgements by decomposing the judgement process after judgements have been rendered. This a posteriori decomposition is accomplished by first using multiple regression analysis to recover prediction equations for both the judgement and ecological systems and then using the Lens Model Equation to compare those systems. SJT methods maintain close contact with ecological circumstances by employing the principle of representative design (which focuses on how the researcher obtains the stimuli for judgement) and avoiding unwarranted over-generalisations from nomothetic aggregation (e.g. averaging across judges) through the use of idiographic–statistical analysis. SJT methods have proven valuable in the analysis of individual judgements as well as group- based judgements where conflict becomes likely. INTRODUCTION Social Judgement Theory (SJT) evolved through the 1960s and 1970s as a methodology and a perspective for understanding human judgement as it was exercised within a particular ecological context (see Doherty, this issue, for greater elaboration on the historical and theoretical underpinnings of SJT). Hammond, Stewart, Brehmer, and Steinmann (1975) considered the theoretical, methodological, and practical implications of SJT, and provided the first relatively complete description of the application of Brunswik’s probabilistic functionalism (with the Lens Model as its conceptual vehicle) and principles of representative design to the study of human judgement. Building on Brunswik’s Requests for reprints should be sent to Ray W. Cooksey, Dept of Marketing and Management, University of New England, Armidale, NSW 2351, Australia.