What makes us believe a conditional? The roles of covariation and causality

Abstract

Two experiments were conducted to investigate the roles of covariation and of causality in people's readiness to believe a conditional. The experiments used a probabilistic truth-table task (Oberauer & Wilhelm, 2003) in which people estimated the probability of a conditional given information about the frequency distribution of truth-table cases. For one group of people, belief in the conditional was determined by the conditional probability of the consequent, given the antecedent, whereas for another group it depended on the probability of the conjunction of antecedent and consequent. There was little evidence that covariation, expressed as the probabilistic contrast or as the pCI rule (White, 2003), influences belief in the conditional. The explicit presence of a causal link between antecedent and consequent in a context story had a weak positive effect on belief in a conditional when the frequency distribution of relevant cases was held constant.

Acknowledgments

This research was supported by Deutsche Forschungsgemeinschaft (DFG, grant FOR 375 1-1). We thank Sonja Geiger, Annekatrin Hudjetz, and Moritz Ischebeck for helpful comments on an earlier draft of this paper. We are especially indebted to Mirko Wendland for posting our experiments on his W-Lab server, http://w-lab.de, and to Ulf Reips for broadly advertising them through his web page, http://www.psychologie.unizh.ch/sowi/Ulf/Lab/WebExpPsyLabD.html

Notes

¹We asked for the probability that the conditional is true in a sample of 50 from the population because it has been argued from a frequentist view of probabilities that probabilities of single events are undefined (Gigerenzer, 1996). Others have asked for the probability of a conditional applied to a single event (Evans et al., 2003), with virtually the same results. We have varied the sample size between 10 and 100 and found little effect on people's estimates of the probability of the conditional (Oberauer, Geiger, Fischer, & Weidenfeld, 2007).