A 19-year-old man presents to the PMHNP for a psychiatric evaluation with a chief complaint of intrusive thoughts and compulsive behaviors. Of the following, which is considered the gold standard assessment tool for obsessive-compulsive disorder (OCD) severity?

Choice A reason: The OCI is a self-report questionnaire that measures OCD symptoms but is less comprehensive than the gold-standard clinician-administered tool. Choice B reason: The FOCI is primarily a brief assessment tool and not widely used as the standard for severity evaluation. Choice C reason: Y-BOCS is the gold-standard clinician-administered scale for measuring OCD severity, assessing both obsessions and compulsions systematically with validated scoring. Choice D reason: The NIMH Global Obsessive-Compulsive Scale is less commonly used and is not considered the gold standard for OCD severity assessment.