Psychometric Validation of the Italian 8-Item Green Paranoid Thoughts Scale (GPTS-8)

Paranoid ideation ranges from mild social-evaluative concerns to persecutory beliefs. The eight-item Green Paranoid Thoughts Scale (GPTS-8) provides a brief assessment of this continuum through reference and persecution items.

To examine the psychometric properties of the Italian version of the GPTS-8, including its factorial structure, reliability, and convergent validity, in a non-clinical university sample.

243 university students completed the Italian GPTS-8 and the Prodromal Questionnaire-Brief (PQ-B). Confirmatory factor analyses compared unidimensional, two-factor, bifactor, and second-order models using maximum likelihood estimation with robust standard errors. Reliability was evaluated using Cronbach's α and McDonald's ω, and item-level contributions to the general factor were examined using bifactor indices (ECV, ωH, IECV).

The bifactor model showed the best fit, supporting a dominant general paranoia factor alongside specific reference and persecution dimensions. Internal consistency was good for the GPTS-8 total score (α = 0.78) and acceptable for the subscales (respectively, 0.68 and 0.66). Item-level diagnostics indicated that several items primarily reflected the general factor, consistent with a hierarchical organization of paranoid ideation. Item response patterns suggested greater sensitivity at moderate to higher levels of the latent trait. Participants scoring above established PQ-B thresholds showed significantly higher GPTS-8 scores across dimensions, supporting convergent validity.

The Italian GPTS-8 showed satisfactory psychometric properties, providing incremental evidence for its structural validity in an Italian-speaking context. However, given the use of a convenience student sample, findings should be considered preliminary and not directly generalizable to broader or clinical populations.