DD is a distinct disorder predicated upon sensitivity to threat and biases of attention and attribution. These findings may have implications for the cognitive therapy of these disorders.

Our findings extend those of others but require cautious interpretation as to the role of probabilistic reasoning in the genesis of delusions or obsessions. Obsessionals in both the OCD and Mixed groups, showed substantial deviation from Bayesian norms, suggesting that obsessionality leads to a reasoning style that is less 'normal' than that of delusionals. Further work is required to investigate clinical correlates of these findings which provide modest support for the proposal that the combination of obsessions and delusions confers greater functional advantages than simply having delusions or obsessions.

Individuals with persecutory delusions have been reported to make external and stable attributions for negative events and to have a tendency towards internal attributions for positive events. It remains unclear whether this abnormality is present in individuals with non-persecutory delusions. Using the Attributional Style Questionnaire, we assessed the attributional style of 19 individuals with persecutory or grandiose delusions (PG), 12 individuals whose delusional beliefs were non-persecutory and non-grandiose (NPG) and 24 controls. The PG group displayed externality in their causal attributions for bad events but those in the NPG group did not differ from controls. Both deluded groups were significantly more stable in their attributions for bad events in comparison to controls. Such findings argue against a primary role for attributional biases in the genesis of delusions, although a role in shaping delusional content and maintaining the disorder and a role for external attributions in defending against reductions in self-esteem cannot be excluded.

We evaluated clinical information gained directly from 10 English-speaking and from 10 non-English-speaking subjects both directly and through interpreter-mediated interviews. High levels of agreement between raters, when assessing both cohorts, were found for all data with a non-significant tendency towards better agreement in the Asian than the English-speaking sample for family history data. Analysis of the interview contents showed a number of errors of interpretation which were similar to those noted in previous studies. The addition of quantitative data representsa significant advantage over previous studies, allowing the qualitative results to be placed into perspective. Recommendations are made for optimising and avoiding the pitfalls of interpreter-mediated interviews.

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