Background. The aims of the study were to investigate whether (i) patients with lifetime presence of non-affective psychosis show an external-personal attribution bias for negative events, (ii) this attribution style can also be detected in first-degree relatives of patients with psychosis and subjects with subclinical psychotic experiences, and (iii) this attribution style is related to the presence of psychotic symptoms, in particular delusions.

Method. Participants were 23 patients with lifetime presence of non-affective psychosis, a high- risk group of 36 first-degree relatives of patients with non-affective psychosis, a high-risk group of 31 subjects with subclinical psychotic experiences and 46 normal controls. Attribution style was measured by the Internal, Personal and Situational Attribution Questionnaire. Positive symptoms were assessed with the Present State Examination (PSE) and the Scale for the Assessment of Positive Symptoms (SAPS).

Results. Relative to the controls, an externalizing bias was apparent in the patient group (β=0·20, p=0·03) but not in the two high-risk groups. There was a dose–response association between externalizing bias and the delusions subscale of the PSE (relative to lowest level: highest level of delusions: β=0·53, p=0·04; intermediate levels of delusions: β=0·23, p=0·35). No significant differences were found in personalizing bias between the four groups.

Conclusions. Patients with psychosis tend to use an externalizing bias in their explanations of negative social events, and this bias is associated with the presence of positive psychotic symptoms, in particular delusions. A deviant attribution style is not part of the vulnerability to psychosis.