Over-adjustment or miscomprehension? A re-examination of the jumping to conclusions bias

Objective: Previous research has consistently shown that individuals with delusions typically exhibit a jumping to conclusions (JTC) bias when administered the probabilistic reasoning 'beads task' (i.e. decisions made with limited evidence or 'premature decisions' and decisions over-adjusted in light of disconfirming evidence or 'over-adjustment'). More recent work, however, also suggests that these effects may also be influenced by miscomprehension of the task. The current paper is an investigation into the contributing effects of miscomprehension on the JTC bias. Method: A total of 75 participants (25 diagnosed with schizophrenia with a history of delusions; 25 non-clinical delusion-prone; 25 non-delusion-prone controls) completed two identical versions of the beads task, distinct only by the inclusion of an extra instructional set designed to increase comprehension. Results: Qualitative data confirmed that miscomprehension is a valid construct, and the results showed that the addition of an instructional set to the second version of the task led to greater comprehension and a statistically significant drop in 'over-adjustment'. Nevertheless, both tasks showed that 'premature decisions' were significantly more prevalent in the schizophrenia group and were unaffected by the intervention. Conclusions: It was concluded that the 'premature decisions' component of the JTC bias remains a feature of decision-making in schizophrenia, but that previously reported 'over-adjustment' effects are likely to be influenced by miscomprehension of the beads task instructional set. These findings are discussed in light of the recently proposed 'hypersalience of evidence-hypothesis matches' account of the JTC bias.