Congruence and discrepancy between self-rated and clinician-rated symptom severity on the Yale–Brown Obsessive-Compulsive Scale (Y-BOCS) before and after a low-intensity intervention

The Yale–Brown Obsessive Compulsive Scale (Y-BOCS) is the most common measure of Obsessive-Compulsive symptom severity. The Y-BOCS interview is considered gold standard, but its self-rating format is increasingly used in clinical trials. Few studies investigated congruency and potential changes over treatment. This question is highly relevant, as a systematic bias might obscure results of clinical trials. We examined the relationship of self- and clinician-rated Y-BOCS scores in participants with obsessive-compulsive disorder in pre (N = 128), post, (4 weeks, n = 104) and follow-up (6 months, n = 98) assessments of a randomized-controlled clinical trial. We administered Y-BOCS interview via telephone paralleling online administration of the self-report form. Analyses showed medium-to-strong correlations of Y-BOCS interview and self-rating scores at pre-assessment. Patients rated symptoms lower than clinicians. Larger discrepancies were associated with hoarding and age. Congruency was inferior for obsessions relative to compulsions, largely owing to the “resistance against obsessions” item. Agreement strongly increased at post and follow-up. Though overall congruency between the two Y-BOCS forms was satisfactory, results suggest a “correction over time” effect. Such bias may distort the precise interpretation of treatment effects. Therefore, we made several suggestions to improve the reliability of change scores assessed with the Y-BOCS self-rating.