| Summary: | We report the development and evaluation of a brief questionnaire measure of persecutory ideation, the Persecutory Ideation Questionnaire (PIQ). Our approach was theoretically driven in that the PIQ was constructed in accordance with comprehensive definitional considerations and criteria set out by Freeman and Garety (2000). Sixty-six more general paranoia-related items were accumulated, and 10 independent raters sorted the items into two sets, persecutory ideation and other. An 80% agreement criterion was set, resulting in 10 persecutory ideation items. The PIQ was evaluated with a nonclinical and a clinical sample. In both samples, it was shown to have excellent reliability (internal consistency) and excellent convergent validity as a measure of certain aspects of general paranoid ideation. Finally, the PIQ shared unique variance with severity of persecutory delusions in the clinical group, providing good criterion validity for the PIQ as a measure of specifically persecutory ideation, rather than paranoia in general.
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