'Attentional Bias' in correlation judgments? Smedslund (1963) revisited

Smedslund (1963) reports one of the first studies that investigated human j udgments of correlation. Smedslund's conclusion, that people reason about c orrelation mostly from a consideration of the number of times two variables co-occur, has become textbook wisdom (e.g. Baron's "attentional bias", 199 4). Yet the data reported in Smedslund's paper fall short of endorsing such a conclusion. After reviewing the original paper, we present the method wi th which we replicated Smedslund's main experiment. In Experiment 1 subject s were presented with symptom-disease correlation data through a simulated medical diagnosis task. Subjects clearly discriminated between data sets wh ich shared an equal number of symptom-disease co-occurrences but which othe rwise showed different levels of correlation. Subjects' diagnoses showed a propensity to predict the disease in the presence of the symptom. and sympt om-disease co-occurrences were overestimated in two of the five data sets p resented to the subjects. Experiment 2 used a novel abstract scenario with a symmetric predictor variable. Judgments again indicated good discriminati on, and biases in prediction responses and case recall were eliminated. In both experiments, judgments of zero correlation were a function of the outc ome base rare. We evaluate and contrast the extent to which Cheng's (1997) model of causal induction and two associative models, Rescorla and Wagner ( 1972) and Pearce (1987) can anticipate the observed pattern in the mean jud gments.