Predictive validity of the overvalued ideas scale: outcome in obsessive–compulsive and body dysmorphic disorders

Overvalued ideas have been theoretically implicated in treatment failure for obsessive–compulsive disorder (OCD). Until recently, there have not been valid assessments for determining severity of overvalued ideas. One recent scale, the Overvalued Ideas Scale (OVIS; Neziroglu, McKay, Yaryura-Tobias, Stevens & Todaro, 1999, Behaviour Research and Therapy, 37, 881–902) has been found to validly measure overvalued ideas. However, its predictive utility has not been determined. Two studies were conducted to examine the extent to which the OVIS predicts treatment response. Study 1 examined the response to behavioral therapy in a group of participants diagnosed with OCD. Residual gain scores showed a significant correlation between treatment outcome for compulsions and pretreatment OVIS scores (28.1% variance accounted). Pretreatment OVIS scores were not significantly correlated with residual gains in obsessions (1.7% variance accounted). The predictive utility of the OVIS was superior to a single item assessment of overvalued ideas available on the Yale–Brown Obsessive Scale in predicting outcome for compulsions. For this item, the variance accounted for compulsions was 6.3% and for obsessions was 3.9%. Study 2 examined the response to behavioral therapy in a group of participants diagnosed with body dysmorphic disorder (BDD), a condition ostensibly linked to OCD and presumed to present with higher levels of overvalued ideas. Residual gains scores showed a significant relationship between obsessions and OVIS (accounting for 34.8% of the variance), but not for compulsions (10.2% variance accounted). As in Study 1, the predictive utility of the OVIS was superior to the single item assessment (with 0.2% variance accounted for compulsions, 2.4% variance accounted for obsessions). Taken together, the studies reported here show that this OVIS is predictive of treatment outcome, and the predictive value depends on which symptoms are used to assess outcome. Further, the scale is more effective in predicting outcome than a widely used single item assessment.