Heterogeneity and dimensional structure of obsessive-compulsive symptoms: implications for the assessment

Analyses of traditional OCD subtypes (washers, checkers, hoarders, etc.) have been criticized for two main reasons. First, OCD symptoms appear to exist on a continuum from subclinical to severe, therefore discrete subtypes may be inadequate to describe this continuum. Second, most OCD patients do not fit neatly into specific symptom categories. Rather, the majority of patients report multiple symptoms of different kinds. Obsessions, compulsions, and avoidance strategies are thematically heterogeneous and tend to reflect the individual’s highly idiosyncratic concerns. Structural analyses indicate that obsessive-compulsive symptoms are dimensional and that particular sorts of obsessions and compulsions tend to co-occur. Therefore, examination of OCD symptom dimensions, rather than symptom subtypes, may be preferable. A dimensional model allows each subject to be rated on the severity, rather mere presence or absence, of a symptom. The heterogeneity and idiosyncratic nature of OCD symptoms present unique challenges to the development of content valid assessment instruments. Although an array of self-report and interview measures have been developed to assess OC symptoms, these measures have a number of important drawbacks: 1) Subjects with multiple types of symptoms will endorse a greater number of scale items and therefore obtain more severe scores. Thus, many existing OC symptom measures confound severity with the range of symptoms present. 2) The vast heterogeneity and idiosyncratic nature of obsessions and compulsions forbids any given self-report measure from including an exhaustive list of these symptoms. 3) Many measures contain a one-dimensional assessment of severity. 4) Existing OCD symptom measures assess obsessions separately from compulsions, as disconnected clinical phenomena. 5) Most measures contain no items assessing avoidance. 6) Most OCD symptom measures include items assessing hoarding, which many authors now consider as a distinct syndrome from OCD. In the present paper, we discuss the implications of these topics for the assessment of OCD and report on the development, evaluation and Italian validation of a new self-report scale—the Dimensional Obsessive-Compulsive Scale (Abramowitz et al., 2010)—which aims to address the aforementioned needs.