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Chapter: Essentials of Psychiatry: Psychiatric Epidemiology

The Epidemiological Catchment Area Study

The basic design involved face-to-face baseline interviews with random samples of adults selected from the catchment ar-eas.

The Epidemiological Catchment Area Study


In response to the 1978 President’s Commission on Mental Health Report, NIMH sponsored the Epidemiological Catch-ment Area (ECA) project to determine the prevalence of mental disorders in specific sites and the proportion receiving mental health services (Regier et al., 1984). Parallel to the planning of the ECA study, the APA published the DSM-III (American Psychiatric Association, 1980), which had clearly defined opera-tional criteria that facilitated case definition. Thus, the concept of a case as a discrete entity that had been achieved in the late 1970s permitted the categorical determination of psychiatric caseness as opposed to the dimensional assessment of symptomimpairment. As a prelude to the ECA, the NIMH cosponsored the development of the Diagnostic Interview Schedule (reviewed above).


The basic design involved face-to-face baseline interviews with random samples of adults selected from the catchment ar-eas, 6-month telephone follow-up interviews to obtain interim information on medical and psychiatric service use, and 1-year face-to-face interviews with the original sample. The initial re-sponse rate ranged from 68% (Los Angeles) to 79% (St Louis and Durham) (Leaf et al., 1991). Overall, 12% of the original re-spondents were lost to or refused to participate in the follow-up interview. Eaton and collaborators (1992) reported that failure to be tracked was associated with being male, young, unmarried and Hispanic; refusal to participate was associated with being older, married and uneducated




Overall, 32.2% of the adults included in the five sites met crite-ria for one or more of the assessed mental disorders during their lifetime (Table 9.2. Phobias and alcohol abuse and dependence were the most common mental disorders (Regier et al., 1985). The lifetime prevalence for phobia was 12.5%, and the 1-month prevalence was 6.2%. The rates for drug abuse and dependence were 5.9% for lifetime and 1.3% for 1-month prevalence.


The ECA study investigators did extensive analyses of the variation in prevalence rates by demographic characteristics




For lifetime diagnosis, 36% of men at some point suffered from an addictive or mental disorder, compared with 30% of women (Table 9.3).


The pooled 1-month prevalence rates for the five sites (see Table 9.4) was 15.4% for all ages for any DSM-III disorder. The age group 25 to 44 years had the highest overall rate of 17.3%. Although this age pattern was also true for women, men aged 18 to 24 years had the highest overall rate. This occurred because of the peak in rates of drug abuse and dependence in men in this age group. Anxiety disorders were most prevalent at 11.7% in women 25 to 44 years old, compared with only 4.7% for men in the same group. The overall prevalence for all affective disorders was 5.1%; the age group with the highest prevalence was women 25 to 44 years old.




Incidence rates were calculated based on the 12-month follow-up assessments of healthy individuals found during the initial as-sessments (Regier et al., 1993).


During the 1-year follow-up period, 6% of the total popu-lation had one or more new disorders (Regier et al., 1993). Also, 5.7% of those with a history of a mental disorder suffered a re-lapse or a new condition in the 1-year period for a total of 12.3% of new cases in 1 year.


Use of Mental Health Services


Although 28.1% of the sample had diagnosable mental or addic-tive disorders, only 14.7% (23 million) received care, indicating that a disproportionate number of individuals suffering from mental and addictive disorders did not receive treatment. Con-versely, although 22% of respondents who had recently used a medical care facility met criteria for a DSM-III disorder, 17% of nonusers had a diagnosable illness (Regier et al., 1993; Eaton et al., 1992; Narrow et al., 1993, Kessler et al., 1987). The dis-orders making the greatest contribution were alcohol abuse and dependence in men and major depression in women. The ECA study found that 0.9% received inpatient treatment in a specialty mental and addictive disorders facility during a 1-year period. Among individuals with any DSM-III disorder who received mental health services, 28.5% sought treatment from either a mental health clinician or medical physician (see Table 9.5).


Comorbidity of Mental and Substance Use Disorders


The ECA study provided valuable data about the prevalence of comorbidity of alcohol and substance use disorders with mental disorders (Regier et al., 1985, 1990). Before the ECA study, most of the information about comorbidity came from populations in treatment settings. Since the early 1950s, it has repeatedly been found that patients in clinical settings typically present them-selves for treatment because they have more than one disorder, a phenomenon first described by Berkson (1946). Thus, clinical populations provide a biased (and inflated) view of comorbidity.


The ECA study defined comorbidity as the occurrence of more than one disorder and did not require that the disorders overlap temporally. Up to 29% of individuals with a mental disor-der suffer from a comorbid substance use disorder. Similarly, in-dividuals with alcohol use disorder have twice the risk of having a comorbid mental disorder and more than five times the risk of having a comorbid drug use disorder. Among individuals with al-cohol use disorders, the most common comorbid mental disorder was anxiety disorder, with a prevalence of 19.4%. For individuals with drug use disorder, 22% suffered from a mental disorder.


In summary, findings from the ECA confirmed the wide-spread and impairing nature of mental disorders reported in the second-generation community studies described above. The methodologic rigor with which the ECA was conducted was in-strumental at dispelling the disbelief and criticism of methodo-logy that frequently accompanied second-generation studies. The rates in the five ECA sites confirmed the high prevalence of untreated mental disorder. ECA results, such as the finding that individuals with mental disorders were relatively more likely to use general medical services compared with those without disor-ders, raised provocative questions for a new generation of psychi-atric epidemiologists.

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