Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication.
Kessler RC, Chiu WT, Demler O, Merikangas KR and Walters EE;
Commented by , 26 Jul 2005
Background
Early epidemiological studies from the 80's and early 90's found high prevalence of mental disorders. The prevalence of mental disorders has not been estimated with the use of DSM-IV and further prior studies have not taking severity into consideration.
Method
Professional interviewers from the Institute of Social Research at the University of Michigan conducted a nationally representative household survey using an expanded version of the Composite International Diagnostic Interview including questions on severity. Disorders were classified into mild, moderate and serious disorders.
Results
A total of 9282 persons agreed to participate in the survey corresponding to 70.9% of the invited sample. The twelve-month prevalence of any disorder was 26.2%. Among these, 59.6% were classified as moderate or serious corresponding to 14% of the population.
Anxiety disorders were the most common disorders with a twelve-month prevalence of 18.1%, and mood disorders were the second most common disorder with a prevalence of 9.5%.
Among anxiety disorders 56.5% were classified as moderate to serious compared to 85% of mood disorders. More than 40% of the 12-months cases were comorbid, and comorbidity correlated strongly with severity.
Professor Kessing's comments
Although the study confirm the prior findings of a high overall 12-month prevalence of mental disorders - 28.1% in the ECA study (ref. 1) and 29.5% in the NCS study (ref. 2) - the study also reveal that only 59.6% of these disorders are of moderate to serious severity corresponding to 14% of the population.
Prior studies found that 55% of the American population will suffer from a mental disorder during lifetime. The present study seems to find similar rates of lifetime mental illness.
However, taking severity into consideration a minor proportion of the population present with a moderate to severe disorder.
The problem is that it is unreasonable to claim that more than half of the American population will suffer from a mental disorder during their lifetime. Presumably, the vast majority of mild disorders represent brief fluctuations in well-being due to mild distress.
The question is whether such fluctuations represent transient symptoms or true disorders or illnesses. The making of DSM-V and ICD-11 warrants an answer to these crucial questions. However, cross-sectional epidemiological studies like the present are not able to answer such questions.
Longitudinal and analytical epidemiological studies are needed to reveal which conditions are mild and transient and which may be precursors of more severe and substantial illness. And for sure psychiatry has to strive for an etiological based diagnostic system eventually, like the rest of medicine (ref. 3).
References
1. Regier DA, Kaelber CT, Rae DS, Farmer ME, Knauper B, Kessler RC and Norquist GS. Limitations of diagnostic criteria and assessment instruments for mental disorders - Implications for research and policy. Arch Gen Psychiatr 1998; 55 (2); 109-115
2. Kessler RC, McGonagle KA, Zhao S, Nelson CB, Hughes M, Eshleman S, Wittchen HU and Kendler KS. Lifetime and 12-month prevalence of DSM-III-R psychiatric disorders in the United States. Results from the National Comorbidity Survey. Arch Gen Psychiatr 1994; 51 (1); 8-19
3. McHugh PR. Striving for coherence: psychiatry's efforts over classification. JAMA 2005; 293 (20); 2526-2528