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To the Editor: Ronald C. Kessler, Ph.D., and colleagues recently reported that among community respondents, generalized anxiety disorder (per the Composite International Diagnostic Interview and DSM-III-R) has a statistically significant independent association with impairment (1). On the strength of this finding, the authors called into question an earlier primary care study in which my colleagues and I used the Structured Clinical Interview for DSM-III-R (SCID); that study indicated that generalized anxiety disorder has only a modest and statistically nonsignificant independent association with impairment (2).
The credibility of the findings reported by Dr. Kessler and co-workers turns on the validity of the Composite International Diagnostic Interview diagnosis of generalized anxiety disorder. In their Method section, they state, "A National Comorbidity Survey clinical reappraisal study found good test-retest reliability and procedural validity of all of the diagnoses compared to clinical reassessments." However, that study found that among sampled respondents to the National Comorbidity Survey, the Composite International Diagnostic Interview diagnosis of generalized anxiety disorder had a kappa of 0.35 with the SCID as the criterion standard (3). In general, kappa values below 0.40 suggest poor agreement beyond chance (4). Moreover, the positive predictive value of a Composite International Diagnostic Interview diagnosis of generalized anxiety disorder was 0.21 (3), meaning that nearly four out of five diagnoses of generalized anxiety disorder were not confirmed with the SCID.
A broader point that is easily overlooked in evaluating findings from large epidemiologic studies is the difference between statistical and clinical significance. Although the differences reported by Dr. Kessler and colleagues are statistically significant, their clinical significance is less clear. More than three-quarters (78.2%) of the group with generalized anxiety disorder reported that they had no days in the last month in which they had to cut back or did not get as much done as usual because of their mental health, and nearly as many (70.7%) reported that their mental health was good to excellent.
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