People who are prone to delusions gather insufficient information before making decisions, according to research published in the journal Psychological Medicine.

Researchers from Royal Holloway, University of London, led by PhD student Leslie van der Leer, assigned participants a computer task in which they observed the color of a black or white fish caught from one of two lakes and were then asked to choose to see further fish or decide on one of the lakes as the source of that sequence of fish.

Each participant was rewarded for choosing the correct lake but costs were imposed for seeing more fish. In addition, the participants completed a questionnaire that measured how prone they were to delusions.

The results showed that the more delusion-prone the participants were, the earlier they chose a lake. Significantly, those who were highly prone to delusions chose a lake in advance of the optimum moment, gathering less information than they needed in order to make the decision that was most beneficial to them.

Dr Ryan McKay, from the Department of Psychology at Royal Holloway, said: "People who suffer from delusions have unjustified, and sometimes bizarre, beliefs about themselves and the world. A tendency to gather insufficient evidence when forming beliefs, and making decisions, is thought to be a core cognitive component of delusion formation.

"In our study, the combination of rewards and costs created optimal decision points, allowing us to investigate genuine 'jumps to conclusions'. Our results confirm that delusion-prone people are less likely to wait for the best moment before making a decision. This indicates that they would rush to make choices in their everyday lives, relating to anything from money or jobs to family and friends, which could lead to less successful outcomes for them."

Dr McKay added that previous studies had only compared the decisions of delusion-prone and non-delusion-prone people to each other rather than to an objective measure of performance: "Surprisingly, our study also found that even low delusion-prone people jumped to conclusions -- so most people jump to conclusions, but delusion-prone people jump further."