Exposure and response prevention (ERP) is primarily deployed by therapists in the treatment of OCD. The American Psychiatric Association (APA) state that CBT drawing primarily on behavioral techniques (such as ERP) has the "strongest evidence base" among psychosocial interventions. By confronting feared scenarios (i.e., exposure) and refraining from performing rituals (i.e., responsive prevention), patients may gradually feel less distress in confronting feared stimuli, while also feeling less inclination to use rituals to relieve that distress. Typically, ERP is delivered in "hierarchical fashion", meaning patients confront increasingly anxiety-provoking stimuli as they progress through a course of treatment.