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Front Psychiatry. 2018 Aug 23;9:390. doi: 10.3389/fpsyt.2018.00390. eCollection 2018.

Stability of the Distribution of Patient Health Questionnaire-9 Scores Against Age in the General Population: Data From the National Health and Nutrition Examination Survey.

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Department of Mental Health Panasonic Health Center, Tokyo, Japan.
Department of Health Promotion and Human Behavior, Kyoto University Graduate School of Medicine School of Public Health, Kyoto, Japan.
Clinical Research Center, Chiba University Hospital, Chiba, Japan.
Department of Pharmacoepidemiology, Graduate School of Medicine and Public Health, Kyoto University, Kyoto, Japan.
Center for the Promotion of Interdisciplinary Education and Research Kyoto University, Kyoto, Japan.
Department of Drug Evaluation and Informatics, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Center for the Development of Cognitive Behavior Therapy Training, Tokyo, Japan.


Background: Epidemiological studies using the nine-item Patient Health Questionnaire (PHQ-9) have reported inconsistencies regarding the relationship between age and total scores. To determine whether this discrepancy is due to the stability of the distribution of PHQ-9 total scores against age, we investigated whether the total score distribution remains stable during adulthood, and also investigated the mathematical patterns of the total score distribution. Methods: The present study utilized data from 15,847 participants of the 2009-2014 United States National Health and Nutrition Examination Survey, all of whom responded to all PHQ-9 items. The stability of the total score distribution among different age groups was examined using overlap coefficients and graphical analysis. Results: High overlap coefficients were observed between all age groups for the distributions of PHQ-9 total scores, suggesting that the distribution of PHQ-9 total scores remains stable against age. Graphical analysis demonstrated that distributions of PHQ-9 total scores were similar across age groups. In addition, distributions of PHQ-9 total scores exhibited an exponential pattern, except at the lower end of the distribution. Conclusions: Our findings indicate that the stability of the distribution of PHQ-9 total scores throughout adulthood may underlie inconsistencies in the evidence regarding age-related changes in total depression scores.


National Health and Nutrition Examination Survey; Patient Health Questionnaire-9; age; depressive symptoms; exponential distribution; overlap coefficients

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