Styles of decision-making and probability appraisal in selected obsessional and phobic patients.

A questionnaire was administered to obsessional and phobic patients and normal subjects. The results of this survey confirmed the prediction that a sizeable proportion of phobic patients report irrational expectations associated with their most feared situations. A group of phobics who reported irrational expectations, a group of obsessionals who reported an abnormal degree of checking behaviour and a group of normal subjects, took part in a probabilistic inference task. Several predictions about the differential performance of these groups were fulfilled. (i) Deviations from the optimal model for individual responses were greatest in the obsessional group. (ii) When Neuroticism was partialled out, the three groups differed with respect to amount of evidence required prior to a decision, the obsessional group having the highest score on this variable. (iii) The phobic group were more likely than the other two groups to make irrational event predictions.