Normative data and psychometric properties of the Patient Health Questionnaire-9 in a nationally representative Korean population

Background The Patient Health Questionnaire-9 (PHQ-9) has been standardized in several populations and is widely used in clinical practice and health care. However, it has not been appropriately standardized in the Korean general population, and no normative data have been presented. The aim of this study was to provide the normative data and psychometric properties of the PHQ-9 in the nationally representative population of Korea. Methods We used the nationwide cross-sectional survey data of Korea from 2014 to 2016. The data of 10,759 individuals aged over 19 years were analyzed in this study. As the distribution of the PHQ-9 scores was not normative, the percentile ranks for raw scores were provided. The survey questionnaires included the PHQ-9, The EuroQol-5 Dimension (EQ-5D), and demographic characteristics. We analyzed the construct validity and internal consistency of the PHQ-9. Results The normative data of the PHQ-9 were generated according to the sex and different age categories. The correlation coefficient between the sum of the PHQ-9 scores and the EQ-5D index was 0.44, which was moderate. The most appropriate model was the two-factor model with five 'affective-somatic' labeled items and four 'cognitive' labeled items. Cronbach's alpha for the PHQ-9 was 0.79. Conclusions Our result supports reliability and validity with two-factor structure of PHQ-9 for measuring depression in the Korean nationally representative population. The Korean normative data on the PHQ-9 according to percentile rank can assist in interpreting and comparing scores with other populations.