Comparing fast thinking and slow thinking: The relative benefits of interventions, individual differences, and inferential rules

Research on judgment and decision making has suggested that the System 2 process of slow thinking can help people to improve their decision making by reducing well-established statistical decision biases (including base rate neglect, probability matching, and the conjunction fallacy). In a large pre-registered study with 1,706 participants and 23,292 unique observations, we compare the effects of individual differences and behavioral interventions to test the relative benefits of slow thinking on performance in canonical judgment and decision-making problems, compared to a control condition, a fast thinking condition, an incentive condition, and a condition that combines fast and slow thinking. We also draw on the rule-based reasoning literature to examine the benefits of having access to a simple form of the rule needed to solve a specific focal problem. Overall, we find equivocal evidence of a small benefit from slow thinking, evidence for a small benefit to accuracy incentives, and clear evidence of a larger cost from fast thinking. The difference in performance between fast-thinking and slow-thinking interventions is comparable to a one-scale point difference on the 4-point Cognitive Reflection Test (CRT). Inferential rules contribute unique explanatory power and interact with individual differences to support the idea that System 2 benefits from a combination of slower processes and knowledge appropriate to the problem.