Psychometric evaluation of the Dutch Persecutory Ideation Questionnaire (PIQ) and its relation to aggression

Patients with schizophrenia and a violent past more often have persecutory delusions than other types of delusions. The main aim of the present study was to examine the relation between persecutory ideation and self-reported aggression in a community based and clinical population. A second aim was to evaluate the psychometric properties of the Dutch version of the Persecutory Ideation Questionnaire (PIQ; McKay, Langdon, & Coltheart, 2006). From the general population, 269 persons were included as well as 79 inpatients from different psychiatric facilities. In the community based sample, the PIQ appeared to be a reliable and valid instrument to measure persecutory ideation. Evaluation of the PIQ in a sample with patients with a psychotic disorder showed that the PIQ had good criterion validity. In addition, results showed that persecutory ideation was significantly related to self-reported aggression in the community based, and in the clinical sample. Moreover, in the community based sample, this association was higher than that between positive psychopathological experiences in general and aggression in the community based sample. In sum, persecutory ideation can be measured reliably with the PIQ, and there seems a robust relation between persecutory ideation in particular and aggression in both clinical and community based samples.