Measuring depression in South Korea: Validity and reliability of a brief questionnaire in the Korean Cancer Prevention Study

Objective: To examine the validity and reliability of a new questionnaire for measuring depression in a South Korean population, and then to estimate the prevalence of depression in that country using this tool. Methods: In total, 742,600 individuals (123,725 women), aged 30-64 years at entry into the Korean Cancer Prevention Study, completed a depression symptom in 1992 (baseline enrollment) and again in 1994. We examined the concurrent validity of the depression questionnaire by relating data from it to known socio-demographic and behavioral correlates of depression; its predictive capacity by relating scores from the questionnaire to the occurrence of future hospitalization for depression; and the test- retest reliability by comparing scores from its administration in 1992 to those in 1994. Results: The prevalence of major depression was 7.5%in men and 10.0%in women. Factors significantly related to major depression were being younger (men), being female, not being married, of lower socioeconomic status, being a smoker, a heavy drinker, and not exercising regularly. Men (hazard ratio; 95%confidence interval: 2.0; 1.8, 2.2) and women (1.6; 1.3, 1.9) with questionnaire-ascertained depression experienced an elevated risk of hospitalization for the disorder during follow-up. The rates of agreement between responses to 1992 and 1994 surveys were 91.3%in men and 88.3%in women. Conclusions: These findings imply validity of the instrument and support its use in future studies directed at links of depression with somatic disease endpoints. Limitation: The questions do not have a specified time frame of reference.