The Changing Prevalence and Severity of Obsessive-Compulsive Disorder
Crino R, Slade T and Andrews G;
Commented by , 30 May 2005
Background
The prevalence rates (life-time prevalence, 12 months prevalence, point prevalence) of obsessive-compulsive disorder (OCD) remain controversial.
Aims of the study
To investigate whether the high prevalence rates that have been reported for OCD in the past 25 years are due, at least in part, to changes in methodology (diagnostic criteria, assessment instruments, definition of disability).
Method
The prevalence and severity of OCD were determined using data from the Australian National Survey of Mental Health and Well-Being. Data included in the analyses came from the assessment of diagnosis (using version 2.1 of the CIDI), the assessment of disability, and the assessment of service use and treatment received. Prevalence rates were computed using DSM-IV diagnostic criteria, and were recalculated using DSM-III criteria.
Results
1 month and 12 months prevalence rates for OCD using DSM-IV criteria were 0.5 and 0.6, considerably lower than expected. Re-assignment of diagnoses according to DSM-III criteria yielded considerably higher 12 months prevalence rates (2.1%). OCD based on DSM-IV criteria was associated with significant degrees of disability and use of service.
Professor Pull's comments
Up to 25 years ago, OCD was considered a rare form of mental disorder. In the years following the publication of DSM-III, results from epidemiologic studies have shown consistently high prevalence rates for the disorder.
As an example, in the Epidemiologic Catchment Area (ECA) study, life-time prevalence of OCD was 2.5%, 12 months prevalence 1.6, and point prevalence 1.2. In the Cross National Collaborative study, life-time prevalence varied between countries from 0.7 to 2.5, and 12 months prevalence from 1.1 to 1.8.
Changes in prevalence rates can be related, to a large extent, to several aspects of methodology. First, and most importantly, to the diagnostic criteria defining OCD. In addition, changes in prevalence rates may be influenced by the type of instrument used for assessing the signs and symptoms defining the disorder (e.g., use of the DIS or the CIDI), and by the type of interviewer (lay interviewers or clinicians) chosen for assessing the signs and symptoms, as well as the severity of the disorder.
The prevalence rates of OCD based on DSM-IV criteria are considerable lower than the rates for OCD based on other diagnostic, in particular DSM-III criteria. As shown by the results of the present study, the difference in prevalence rates can be attributed to differences in the diagnostic criteria used to define the disorder.
The DSM-IV diagnostic criteria identify a more severe or "core" type of the disorder. This type is associated with considerable co-morbidity (in particular with regard to mood disorders, other anxiety disorders and substance use disorders), as well as with significant impairment and service use.
Other definitions of OCD, using broader diagnostic criteria, probably include less severe or threshold types of the disorder, or disorders that are currently thought of as possibly belonging to a "spectrum" of obsessive-compulsive disorders.
Broad definition? Narrow definition? The question is still open to debate. Additional empirical studies (in particular genetic and brain imaging studies) are needed to determine what diagnostic criteria are the most valid.