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National Institutes of Health

Questions and Answers about the National Comorbidity Survey Replication (NCSR) Study

Q: What makes the National Comorbidity Survey- Replication (NCS-R) different from previous large-scale epidemiological studies on mental health?

A: From 1980 to 1985, the National Institute of Mental Health’s (NIMH) Epidemiologic Catchment Area (ECA) program surveyed 20,000 people selected from five different U.S. geographic regions. Mental disorders were classified according to the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III). The ECA was limited by the inability to generalize data gathered from its five study sites to describe the state of mental health on a broader scale. The second study, the predecessor to the current study, was the National Comorbidity Survey, an analysis of a nationally representative sample of the U.S. conducted from 1990-1992, which used a revised survey called the World Health Organization (WHO) Composite International Diagnostic Interview (CIDI). It was designed to assess mental disorders based on the updated disease categories of the revised DSM-III, or DSM-III-R.

In the third study, the NCS-Replication (reported in the June 6, 2005 issue of the Archives of General Psychiatry) researchers studied a new nationally representative sample of the U.S. population, repeating many of the questions from the original NCS and expanding the original study’s scope by incorporating updated disease assessment criteria based on the Fourth Edition of the DSM (DSM-IV). The goal was to uncover trends in mental health prevalence, impairment, and service use over the decade of the 1990s. In addition, data were collected in accordance with the World Health Organization’s (WHO) World Mental Health Survey Initiative, which seeks to gather reliable, cross-national analyses of mental, substance use, and behavior disorders in 28 countries, representing all WHO regions; these efforts will help validate the estimates of mental health burden, identify barriers to service, and evaluate intervention targets on a worldwide scale.

Q: How is the study population “nationally representative”?

A: There is a growing gap between the characteristics of people with mental disorders who are identified in treatment settings and those with mental disorders in the general population. One of the most important findings from psychiatric epidemiology is the extent to which people with severe mental disorders never come to the attention of mental health professionals. By gathering data through face-to-face, household interviews, the NCS-R researchers were able to obtain accurate estimates of the proportion of people who obtain treatment according to the severity of their disorder and the type of treatment that they received.

Q: What is the difference between “12-month prevalence” and “lifetime prevalence” referred to throughout the NCS-R?

A: “Twelve-month prevalence” refers to the proportion of study participants who identified symptoms occurring in the 12 months preceding the study interview that could be categorized as a mental health disorder. “Lifetime prevalence” was estimated based on the proportion of respondents who had ever had a mental disorder at the time of the interview.

Q: How is “adequacy of treatment” defined in the NCS-R papers?

A: The NCS-R evaluated mental health treatment in terms of minimal adequacy according to recommendations and guidelines from the American Psychiatric Association (APA) and the Agency for Healthcare Research and Quality (AHRQ). For example, minimally adequate treatment for major depressive disorder (MDD) was defined as receiving either four or more outpatient visits with any type of medical doctor and prescription of an antidepressant or mood stabilizer for at least 30 days; or receiving eight or more psychotherapy sessions lasting a minimum of 30 minutes each. The determination of minimally adequate treatment varied for different disorders. In general, complementary and alternative medicine and non-medical human services (social work, religious/spiritual guidance, etc.) were not considered adequate treatment based on the lack of supporting experimental data.

Q: What are the public health implications of the papers’ findings with regard to treatment?

A: Overall, 6 percent of mental illnesses are severely debilitating; the delay from onset until treatment is 6 to 23 years. Treatment rates are somewhat higher now than a decade earlier. However, there is still much to be done to ensure that people with mental disorders receive timely and effective treatment. Nearly 60 percent of people with active mental disorders seek no treatment in the prior year. Existing therapies still need to be more widely disseminated; and because existing therapies do not work for all people, a new range of therapies is needed. New programs are also needed to increase timely initiation of treatment, especially in underserved areas. New initiatives are needed to ensure these model programs are widely used by patients, clinicians, and health plans. In addition, more research is required on early intervention; for instance, when is the best time to intervene in order to prevent the progression of illness and co-morbidities from developing? Investigation must continue to determine risk profiles, or when a person is likely to move from a mild disorder to a severe one.

Q: The study found a high degree of co-morbidity; what does this mean and what are the implications?

A: Comorbidity refers to the co-occurrence of disorders within the same individual. The study determined that 45 percent of those with one mental disorder met criteria for two or more disorders. We have a limited ability to draw clear-cut thresholds beyond which an emotion or behavior becomes a disorder, and boundaries between types of disorders. In addition, severity of mental illness, in terms of disability, is strongly related to comorbidity.

Other research projects show that substance use disorders are often a consequence of primary mental disorders such as anxiety or bipolar mood disorders, which often begin in adolescence or young adulthood. Intervening with the primary disorder may help prevent the subsequent development of drug abuse. Although mental disorders and substance use disorders often appear together, services for them are often separate. Study findings highlight the importance of integrating services for people with comorbid mental and substance use disorders, particularly among those with serious mental illness who may be less able to seek appropriate help.

Q: What are the most common mental disorders in the United States?

A: The three most prevalent 12-month disorders found by the NCS-R were specific phobia (9 percent), social phobia (7 percent), and major depressive disorder (7 percent). The most prevalent 12-month disease classes are anxiety disorders (18 percent), mood disorders (10 percent), impulse-control disorders (9 percent), and substance disorders (4 percent). The most prevalent lifetime disorders are anxiety disorders (29 percent), mood disorders (21 percent), impulse-control disorders (25 percent), and substance use disorders (15 percent).

Many of these disorders are described in the Health Information section of the NIMH website.

Q: What mental disorders are the most severe?

A: The mental disorders with the highest proportion of seriously disabling 12-month cases are: bipolar disorder (83 percent); drug dependence (57 percent); and obsessive-compulsive disorder (51 percent). Interestingly, impulse-control disorders, which have been neglected in most previous epidemiological studies of adults, have a greater proportion at the serious level than either anxiety disorders or substance use disorders.

Q: What makes a disorder “severe,” as opposed to “moderate” or “mild?”

A: Severe disorders were defined as cases which had any of the following: suicide attempt within the preceding 12 months with serious lethality intent; work disability or substantial limitation due to a mental or substance disorder; psychosis; bipolar I or II disorder; substance dependence with serious role impairment (as defined by disorder-specific impairment questions); an impulse-control disorder with repeated serious violence; or any disorder that resulted in an inability to function in a particular social role for 30 or more days in the year. Cases were defined as moderate if they had any of the following: suicide gesture, plan or ideation; substance dependence without serious role impairment; at least moderate work limitation due to a mental or substance disorder; or any disorder with at least moderate role impairment in two or more domains of the Sheehan Disability Scales. All other cases were classified mild.

Q: How early can mental illness develop?

A: The median age of onset for anxiety disorders (age 11) and impulse-control disorders (age 11) is much earlier than for substance use disorders (age 20) and mood disorders (age 30). Furthermore, for the majority of cases of impulse-control, substance use, and anxiety disorders, the age of onset is confined to a relatively limited range — most cases of impulse-control disorder occur between age 7-15; substance use disorders between age 18-27; anxiety disorders between age 6-21; these are compared to mood disorders, which have a 25 year range (age 18-43). Individuals with comorbid disorders tend to have had an earlier onset of the first disorder than those who only have one mental disorder.

Q: What other such studies are being done and what will they tell us?

A: Two additional minority-specific psychiatric epidemiology studies are linked to the NCS-R: the National Survey of African Americans (NSAA) and the National Latino and Asian American Study (NLAAS). These studies have also been conducted using nationally representative samples and include diagnostic, pharmacologic and service use modules that are consistent with the NCS-R, as well as scales that measure culture specific constructs among the minority groups.

A final feature of the mental health survey project is the adolescent instrument attached to the NCS-R and the NSAA. Recognizing the need for mental health, risk factor and service need/use information about our nation’s youth, NIMH took advantage of this field opportunity to add a comprehensive adolescent component to total project. A total of 10,000 youth ages 13-18 will be drawn from a school sample (approximately 75 percent) and the existing household sample (25 percent — to cover youth who do not attend school). As with the adult surveys, the adolescent survey assesses mental and physical health, impairment/disability, and patterns of service use. In addition, an extensive risk factor battery and parent questionnaire has been incorporate