High prevalence estimates in epidemiological surveys have led to concerns that the DSM system is overly inclusive and that mild cases should be excluded from future DSM editions.
To demonstrate that the DSM-III-R disorders in the baseline National Comorbidity Survey (NCS) can be placed on a severity gradient that has a dose-response relationship with outcomes assessed a decade later in the NCS follow-up survey (NCS-2) and that no inflection point exists at the mild severity level.
The NCS was a nationally representative household survey of DSM-III-R disorders in the 3-year time span 1990-1992. The NCS-2 is a follow-up survey of 4375 NCS respondents (76.6% conditional response rate) reinterviewed in 2000 through 2002. The NCS-2 outcomes include hospitalization for mental health or substance disorders, work disability due to these disorders, suicide attempts, and serious mental illness.
Twelve-month NCS/DSM-III-R disorders were disaggregated into 3.2% severe, 3.2% serious, 8.7% moderate, and 16.0% mild case categories. All 4 case categories were associated with statistically significantly (P<.05, 2-sided tests) elevated risk of the NCS-2 outcomes compared with baseline noncases, with odds ratios of any outcome ranging monotonically from 2.4 (95% confidence interval, 1.6-3.4) to 15.1 (95% confidence interval, 10.0-22.9) for mild to severe cases. Odds ratios comparing mild to moderate cases were generally nonsignificant.
There is a graded relationship between mental illness severity and later clinical outcomes. Retention of mild cases in the DSM is important to represent the fact that mental disorders (like physical disorders) vary in severity. Decisions about treating mild cases should be based on cost-effectiveness not current severity. Cost-effectiveness analysis should include recognition that treatment of mild cases might prevent a substantial proportion of future serious cases.