The Nepean Belief Scale: preliminary reliability and validity in obsessive-compulsive disorder.

Objectives: To examine the psychometric characteristics of the Nepean Belief Scale (NBS), a short clinician-administered scale that assesses the characteristics and intensity of beliefs in obsessive-compulsive disorder (OCD).

Methods: The NBS was administered by two clinicians to 27 subjects with OCD as part of a larger study that included a comprehensive assessment using the Yale-Brown Obsessive Compulsive Symptom Scale (Y-BOCS), the Overvalued Ideas Scale (OVIS) and the Symptom Checklist 90-Revised (SCL-90R). Test-retest reliability of the NBS was assessed by administering the scale 5 days after initial administration.

Results: The 5-item NBS proved easy to use with an assessment time of less than 5 min. Its interrater reliability revealed 99.5% concordance, while the kappa for test-retest reliability was 0.98 (95% CI = 0.95-1.00). Cronbach alpha coefficient for internal consistency was 0.87. The NBS was found to have excellent convergent and discriminant validity.

Conclusions: Preliminary results suggest that the NBS could be a useful shorter alternative to the currently more widely used instruments for assessing beliefs such as the OVIS and the Brown Assessment of Belief Scale. The NBS has clear instructions and definitions, excellent interrater reliability and convergent validity, and it more accurately measures belief-related insight.