Diagnostic Performance of the Turkish Version of the Vancouver Obsessional Compulsive Inventory (VOCI) Versus Padua Inventory-Revised (PI-R): a Validation Study

Abstract

Objective: The Vancouver Obsessional Compulsive Inventory (VOCI) is a self-report inventory developed to assess a wide range of obsessive-compulsive symptoms, including contamination (12 items), checking (6 items), obsessions (12 items), hoarding (7 items), just right (12 items), and indecisiveness (6 items). The English version of the VOCI has been shown to be a promising psychometric instrument, as have its French, Italian, and Spanish versions. The aim of this study was to investigate psychometric properties of the Turkish version of the VOCI in clinical and non-clinical samples. Method: A questionnaire package including the VOCI, Padua Inventory-Revised (PI-R), Obsessional Beliefs Questionnaire (OBQ), and Beck Depression Inventory (BDI) was administered to volunteer undergraduates (n=365) and patients with obsessive-compulsive disorder (OCD) (n=46). Psychometric analyses were run to assess reliability and validity of the Turkish version of the VOCI. We converged a confirmatory factor analysis to test the factor structure. We also performed a receiver operating characteristic (ROC) analysis to determine cut-off scores and compared the diagnostic performance of the VOCI and PI-R. Convergent and discriminant validity of the VOCI were assessed through Pearson product-moment correlation coefficients. Internal consistency and temporal reliability were computed. Results: Confirmatory factor analysis replicated the original six-factor structure. The maximum likelihood factor loading estimates were higher than 0.40. OCD patients scored significantly higher than control subjects on the contamination, checking, obsessions, things just right, and indecisiveness subscales of the VOCI but not on the hoarding subscale. The global VOCI scores highly correlated with the PI-R (r=0.89); correlation between the contamination subscale of the VOCI and washing subscale of the PI-R was r=0.88; correlation between the checking subscales of both screening tools was r=0.83; correlation between the just right subscale of the VOCI and precision subscale of the PI-R was r=0.71; and correlation between the obsession subscale of the VOCI and rumination subscale of the PI-R was r=0.71. Divergent validity of the VOCI was also high, so that correlations of the total and subscales of the VOCI with the total and subscales of the PI-R were from r=0.25 to a high of r=0.41; therefore, it can be said that the coefficients ranged from weak to moderate. These correlation coefficients were indicative of good convergent and divergent validity. Internal consistency of the VOCI global was 0.97, and that of the VOCI subscales ranged between 0.82 and 0.92 in the overall sample. Cronbach's Alphas of the VOCI subscales in the OCD group were between 0.73 and 0.88, and in the control group between 0.84 and 0.92. Fifteen-day test-retest intra-correlations for total scores of the VOCI were 0.75; for the subscales they ranged from 0.68 up to 0.88. The ROC analysis demonstrated a moderate diagnostic performance for the VOCI cut-off score of 87.5 with a sensitivity of 0.74 and a specificity of 0.73 immediately comparable to the PI-R cut-off point of 67.5. Conclusion: The VOCI had good internal consistency, test-retest reliability, convergent and discriminant validity. It is concluded that the Turkish version of the VOCI has sound psychometric properties. Further studies are needed to develop psychometric tools with stronger diagnostic performance for OCD assessment.