Illusory Correlation and the Inverse Base Rate Effect: Different Underlying Mechanisms

The two phenomena of illusory correlation and the inverse base rate effect are both misperceptions of true contingencies and are evoked by training procedures with analogous structures. We therefore explored the possibility that they share a common underlying mechanism. In two experiments using social stimuli (traits and groups), we measured illusory correlation and the inverse base rate effect in a within-subjects design. We found no hint of correlation in their magnitudes, which suggests that the two effects are generated by different mechanisms. In Experiment 2, we gave no explicit feedback for the rare cue in illusory correlation, yet robust illusory correlation was obtained. This suggests that illusory correlation is a response strategy, not a learning effect. Previously established mathematical models of attentional learning and eliminative inference (a response strategy) were fit to the data via computer simulations. The attentional learning model could accurately fit the inverse base rate effect, but fared less well for illusory correlation. The eliminative inference model fit the illusory correlation results better than the inverse base rate effect. We conclude that while the two phenomena are dominated by different underlying mechanisms, both mechanisms may be at work in social situations.