OCD severity for the worst episode was assessed using the Yale–Brown Obsessive Compulsive Scale (YBOCS) (Goodman et al. 1989). Severity ratings for specific symptom dimensions were determined as described previously using the YBOCS Symptom Checklist (YBOCS-CL) to score each of four factors: forbidden thoughts (aggressive, religious, and sexual obsession categories), symmetry (symmetry obsessions, checking, counting, ordering, and repeating compulsion categories), cleaning (contamination, somatic obsessions, and cleaning compulsion categories), and hoarding (hoarding obsession/compulsion categories) (Bloch et al. 2008).
