A Clinical Significance Criterion Is Essential for Diagnosing Subthreshold Depression

To the Editor: In the March 2010 issue of the Journal, Jerome C. Wakefield, Ph.D., D.S.W., et al. (1) examined the redundancy thesis of the DSM-IV clinical significance criterion for major depression. The authors highlighted that the introduction of a clinical significance criterion does not meaningfully alter the prevalence rates of major depression, regardless of whether a clinical significance criterion with a low or high threshold is used. Furthermore, they concluded that the use of a clinical significance criterion for subthreshold depression is questionable, since "virtually all individuals reporting extended sadness also reported significant distress" (1, p. 302).

However, the conclusions for subthreshold depression were drawn on the basis of a questionable definition of clinical significance. Dr. Wakefield et al. (1) defined clinically significant distress or impairment as reporting some distress or impairment, which constitutes a low threshold for clinical significance. Different from major depression, clinical significance is not already an inherent part of the symptom cluster of subthreshold depression because of the low number of symptoms needed for the diagnosis. Hence, the low threshold of clinical significance conflicts with the purpose of a clinical significance criterion to reduce the risk of pathologizing human behavior. Using data of a general population survey, one recent study (2) demonstrated that the prevalence rates of subthreshold depression based on a clinical significance criterion with a low threshold (Munich-Composite International Diagnostic definition of clinical significance) were approximately equal to those obtained by using a cut-off score of 49 on the Short Form-36 Mental Component Summary score. Considering that a Mental Component Summary score of 50 represents the mean score of the general population, a low threshold of the clinical significance criterion seems inappropriate. It is crucial to define a threshold for clinical significance, which distinguishes persons whose level of distress reflects common human behavior from persons whose level of distress justifies a subthreshold diagnosis (2–4).

Using a higher threshold, Dr. Wakefield et al. (1) showed that 43.5% of all respondents who reported non-major depression sadness did not report severe distress. This high reduction of subthreshold cases by using a higher threshold for clinical significance corresponds with the aforementioned study (2), which highlighted that only 26.5%–61.1% of subthreshold diagnoses remain valid, if any clinical significance criterion is used in addition to a symptom count. Thus, the risk of pathologizing the general population is significantly reduced when a clinical significance criterion is taken into account. Diagnosing subthreshold depression is therefore a question of an appropriate threshold rather than a question of whether or not a clinical significance criterion is necessary (2–4).