We have explored functional impairment and quality of life across the spectrum of depressive symptoms. The sample studied here was randomly chosen from information provided by an urban community mental health center in Seoul, and the response rate was quite robust; thus, it is likely that the results reflect the general characteristics of the adult metropolitan population of Korea.
The main findings of this study were that significant depressive symptoms that did not meet criteria for a DSM-IV diagnosis of major depressive disorder or dysthymic disorder were very prevalent among the community-dwelling adult population. In this study, the prevalence rates of major depressive disorder and dysthymic disorder were similar to the 12-month prevalence rates of these 2 disorders reported in a nationwide study (2.5% and 0.3%, respectively) despite the differences in interviewing tools (3
). The prevalence of depressive symptoms was much higher: 1 in every 6 (approximately 17%) of the study subjects reported having significant depressive symptoms. This means that only 17% of subjects with significant depressive symptoms can be diagnosed as having a disorder, according to the DSM-IV.
These depressive symptoms inflicted significant functional loss, even when a formal diagnosis could not be made. The loss of work days in the depressive disorder group was 7.4 days per month on average, comparable with the 6.2 days from an earlier Korean report utilizing the CIDI and WHODAS II (25
). However, even without a formal depressive disorder diagnosis, depressive symptoms were related to a higher loss of work, and in the pentagonal graph of functional impairment and quality of life status (), the depressive symptom group seems closer to the depressive disorder group, rather than the normal group. Thus, depressive symptoms that fail to reach a "disorder" status clearly still have both clinical and public health significance. This finding would justify interventions for those who do not meet the diagnosis for a DSM-IV disorder, but are still complaining of depressive symptoms. Of note, the average number of work loss days of those with major depressive disorder, according to the National Comorbidity Study (NCS) in the USA, was 2.6 days per month, indicating that in this study, the level of disability from major depressive disorder in Korea was quite high.
This finding is in line with previous studies exploring subthreshold depression or minor depressive disorder. Although not many studies have explored the quality of life and work functioning of those with subthreshold depression, there is growing evidence that depressive symptoms might be a risk factor for developing major depressive disorder (14
), and they might also have significant psychosocial impairment (27
). In addition to the adult population, there are also growing concerns about the significance of subthreshold depression in both the adolescent (28
) and elderly populations (29
This significant disability due to subthreshold depression would be especially relevant in Korea. There might have been problems related to interviewing with trained but non-professional interviewers and the strictness of the CIDI criteria used in previous nationwide studies. However, in our study, the final diagnosis was made by a clinical diagnosis and the much less structured MINI-K, and the prevalence of depressive disorders was still low. In contrast, the prevalence of positive depressive symptoms was not low; we found it to be around 16.3%, according to the CES-D scores. Furthermore, we used a CES-D cut-off point of 21, which has been reported as optimal in Korea (18
), but as other countries generally use cut-off points of around 16, the results between the present study and previous studies in other countries cannot be compared directly. However, a large nationwide community study using the CES-D in Korea had a cut-off score of 16, and reported that 25.3% of the sample had depressive symptoms (11
); they pointed out that this was a higher prevalence than most reports from other countries that had a cut-off of 16.
These findings might constitute a "categorical fallacy" in the diagnosis of depressive disorders in the Korean population. Current operational criteria like the DSM-IV and ICD-10 are both categorical diagnosis. Subjects can only be classified as having a disorder or not. Screening questionnaires like CES-D are dimensionally oriented. The total score of questionnaires can be interpreted as a seriousness of symptoms. It is still debatable which approach-categorical or dimensional-is preferable for diagnosing common mental disorders (10
). Our findings support the spectrum or dimensional approach to depressive illness, at least for community residents. One earlier study utilizing CES-D compared the usual simple scoring method for the CES-D with alternative scoring method, in which only "persistent" symptoms are counted in yes/no fashion. This categorical method using "persistence" is similar to the method used in DSM-IV or ICD-10. The study concluded that in a community, using the simple score method (e.g. dimensional approach) is more useful than categorical method (30
). Indeed, the frequent "psychiatric comorbidity" among common mental disorders makes formal diagnostic criteria like the DSM-IV or ICD-10 less useful; in addition, many clinicians rely on symptom profiles rather than a strict diagnosis by formal criteria in deciding treatment options. However, health insurance and government policies still adhere to these diagnostic criteria, and these discrepancies between policy and clinician experience have created much confusion in the field. Some government officials and public media seem to discredit depressive disorder as an important cause of suicide because of the low prevalence of "formal" depressive disorders according to nationwide studies.
There are a few limitations in this study. Firstly, we performed a diagnostic interview only for subjects with CES-D scores over 21. We did this according to a recommendation from an earlier study about the use of the CES-D as a screening tool in a community (18
), but we still might have missed people who could be diagnosable as having a depressive disorder, especially those who fell within the CES-D range of 16 to 21. However, since there were only 3 cases of major depressive disorder and 1 case of dysthymia according to the MINI-K results among subjects with CES-D scores below 21, this likely did not affect the results considerably. Secondly, as a cross-sectional study, we cannot really ascertain whether the disability and loss of quality of life was the result or the cause of the depressive symptoms or depressive disorders. Further longitudinal research is needed to elucidate the cause-effect relationship between depressive symptoms and disability.
In conclusion, significant depressive symptoms below the threshold of a DSM-IV diagnosis of major depressive disorder or dysthymic disorder are prevalent in Korea, and cause substantial loss of everyday functions and quality of life in community. Only a small proportion of these depressive subjects in community can be diagnosed as having a DSM-IV depressive disorder. This study provides some evidence favoring the dimensional approach to common mental disorders in community, and also supports the need for public mental health initiatives including early screening, education, and psychiatric interventions targeting subjects with mild depressive symptoms.