Distributional patterns of item responses and total scores on the PHQ-9 in the general population: data from the National Health and Nutrition Examination Survey

Shinichiro Tomitaka, Yohei Kawasaki, Kazuki Ide, Maiko Akutagawa, Hiroshi Yamada, Yutaka Ono, Toshiaki A. Furukawa

Recently, item responses and total scores on depression screening scales have been reported to have characteristic distributions in the general population. The distributional pattern of responses to the Patient Health Questionnaire-9 (PHQ-9) in the general population has not been well studied. Thus, we carried out a pattern analysis of the PHQ-9 item responses and total scores in US adults. Data (5372 individuals) were drawn from the 2013-2014 National Health and Nutrition Examination Survey in the United States. The item responses and total score distributions of the PHQ-9 data were investigated with graphical analysis and exponential regression model. Lines of item responses showed the same pattern among the nine items, characterized by crossing at a single point between "not at all" and "several days" and a parallel pattern from "several days" to "nearly every day" on a log-normal scale. The total score distribution of the PHQ-9 exhibited an exponential pattern, except for at the lower end of the distribution. The present results support that the item responses and total scores on the PHQ-9 in the general population show the same characteristic patterns, consistent with the previous studies using the Center for Epidemiologic Studies Depression Scale (CES-D) and Kessler Screening Scale for Psychological Distress (K6).