Delusion-proneness or miscomprehension? A re-examination of the jumping-to-conclusions bias


Ryan Balzan, BPsych (Hons), School of Psychology, Hughes Building, The University of Adelaide, Adelaide, SA 5005, Australia. Email:


Previous research has consistently shown that individuals with delusions typically exhibit a jumping-to-conclusions (JTC) bias when administrated the probabilistic reasoning ‘beads task’ (i.e., decisions made on limited evidence and/or decisions over-adjusted in light of disconfirming evidence). However, recent work in this area has indicated that a lack of comprehension of the task may be confounding this finding. The purpose of the present study was to evaluate the influence of task administration, delusion-proneness, and miscomprehension on the elucidation of the JTC bias. A total of 92 undergraduate university students were divided into one of two task conditions (i.e., non-computerised and computerised) and were further identified as either delusion-prone or non-delusion-prone and as comprehending or non-comprehending the task. Overall, 25% of the sample demonstrated a JTC bias, and just over half made illogical responses consistent with a failure to comprehend the task. Qualitative evidence of comprehension revealed that these ‘illogical responses’ were being driven by a misunderstanding of task instructions. The way the task was administrated and levels of delusion-proneness did not significantly influence JTC. However, miscomprehending participants were significantly more likely to exhibit the bias than those who did comprehend. These results suggest that miscomprehension rather than delusion-proneness may be driving the JTC bias, and that future research should include measures of miscomprehension.