Reinterpreting illusory correlation: From biased covariation to meaningful categorisation

The illusory correlation effect has traditionally been conceived as an irrational information processing bias arising form the greater attention or weight accorded to infrequent and thus distinction co-occurrences (Hamilton & Gifford, 1976). Alternative explanations for this effect are considered and we outline our own program of research showing that illusory correlation can arise from a process of category differentiation which builds on real contrasts in the stimuli (cf. McGarty, Haslam, Turner & Oakes, 1993). We analyse the role played by the contextual features of the task in facilitating categorisation and specifically examine the effects of the instructions, the form and content of the stimuli, and degree of cognitive load on illusory correlation. We present a processing model summarizing the effects of these factors, and conclude that although illusory correlation can be seen as a biased product, there is much evidence that it derives from a rational and functional sense-making process.