Further Validation of the Persecutory Ideation Questionnaire in the Italian Context: Results From Classical and Modern Test Theory

The Persecutory Ideation Questionnaire (PIQ) is a valuable instrument to measure persecutory ideation. The aim of this study is to validate the scale in the Italian context and to extend the study of its psychometric properties using approaches from both classical and modern test theories. The results of the study, involving 700 individuals, confirmed the one-factor structure and the good validity and reliability of the scale. Full metric invariance and partial scalar and strict invariance were also supported across gender, age, and education level groups. Rasch analysis indicated that the 5-point response scale is well-functioning and that the PIQ is most appropriate to measure high levels of persecutory ideation. The results contribute to a better understanding of the measurement properties of the PIQ. The paper discusses the advantages and contributions of each method used to explore the measurement properties of the scale.