title: A distribution model of the responses to each depressive symptom item in a general population: a cross-sectional study.
abstract: OBJECTIVE
  Some researchers have reported that distribution of total depressive symptom scores in the general population may follow an exponential pattern except at the lowest end of the scores. To understand the mechanism responsible for this phenomenon, we investigated the mathematical patterns of the individual distributions for each item of a depressive symptom scale.
  
  
  METHODS
  We analysed data from 32,022 participants in the general population who participated in the Active Survey of Health and Welfare, Japan. Depressive symptoms were assessed using the Japanese version of Center for Epidemiologic Studies Depression Scale (CES-D). CES-D has 20 items, each of which is scored in 4 grades: 'Rarely', 'Some', 'Much' and 'Most of the time'.
  
  
  RESULTS
  The individual distributions of 16 negative items belonging to the depressive mood, somatic symptoms and retarded activities, and interpersonal relations categories, followed a common mathematical pattern, which displayed different distributions with a boundary at 'Some'. The distributions for the 16 items between 'Rarely' and 'Some' appeared to cross at a single point. On the other hand, the distributions of the 16 items between 'Some' and 'Most' followed a linear pattern when plotted using a log-normal scale. The remaining 4 items in the positive affect subscale showed non-specific patterns.
  
  
  CONCLUSIONS
  The common mathematical pattern of the 16 negative item distributions may contribute to the exponential pattern of the distribution of total depressive symptom scores except at the lowest end of the scores.
authors.affiliation: Department of Mental Health, Panasonic Health Center, Tokyo, Japan Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Tomitaka
authors.affiliation: Department of Drug Evaluation and Informatics, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Kawasaki
authors.affiliation: Department of Health Promotion and Human Behavior, Department of Clinical Epidemiology, Kyoto University Graduate School of Medicine/School of Public Health, Kyoto, Japan.
authors.forename: Toshiaki
authors.identifier: http://orcid.org/0000-0003-2159-3776
authors.initials: T
authors.lastname: Furukawa
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003430:Cross-Sectional Studies; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011569:Psychiatric Status Rating Scales; D057566:Self Report; D012720:Severity of Illness Index; D017678:Sex Distribution; D055815:Young Adult
keywords: EPIDEMIOLOGY; STATISTICS & RESEARCH METHODS