Single or Dual Processing in Base-Rate Problems? Using Signed Difference Analysis to Test the Distinction

Abstract

When reasoning on classic base-rate problems, people's judgements often underweight base-rate information and rely heavily on stereotype information. These patterns of performance have been shown to vary according to cognitive ability. Single- and dual- process theories are two competing classes of theory that have been applied to explain the impact of cognitive ability on base-rate task performance. Dual-process theories propose that low and high cognitive ability individuals differentially rely on two distinct processes to evaluate base-rate problems: one that is more readily deployed and based more on stereotypes (Type 1 processing), and one that is less readily deployed and based more on base-rates (Type 2 processing). In contrast, single-process theories suggest that both low and high ability individuals draw on a common type of processing that integrates both base-rate and stereotype information. To help adjudicate between the competing theories, the current study instantiated them as formal Signal Detection models and rigorously tested their predictions against novel base-rate reasoning data using Signed Difference Analysis (SDA). In an online experiment, 101 participants completed a base-rate task that included several within-subjects' manipulations designed to probe dual-process assumptions (e.g., base-rate ratio), then completed two cognitive ability tasks (Raven's matrices and operation span). The results of the cognitive ability tasks were used to categorise participants into low or high ability for later analysis as a between-subjects factor. Consistent with dual-process predictions, high ability participants were more sensitive to base-rate information than low-ability participants. However, SDA revealed that the single-process model was also consistent with the data. This finding demonstrates the viability of a single-process theory of base-rate insensitivity and further challenges the value of standard dual-process views of the phenomenon.