title: Pattern analysis of total item score and item response of the Kessler Screening Scale for Psychological Distress (K6) in a nationally representative sample of US adults.
abstract: BACKGROUND
  Several recent studies have shown that total scores on depressive symptom measures in a general population approximate an exponential pattern except for the lower end of the distribution. Furthermore, we confirmed that the exponential pattern is present for the individual item responses on the Center for Epidemiologic Studies Depression Scale (CES-D). To confirm the reproducibility of such findings, we investigated the total score distribution and item responses of the Kessler Screening Scale for Psychological Distress (K6) in a nationally representative study.
  
  
  METHODS
  Data were drawn from the National Survey of Midlife Development in the United States (MIDUS), which comprises four subsamples: (1) a national random digit dialing (RDD) sample, (2) oversamples from five metropolitan areas, (3) siblings of individuals from the RDD sample, and (4) a national RDD sample of twin pairs. K6 items are scored using a 5-point scale: "none of the time," "a little of the time," "some of the time," "most of the time," and "all of the time." The pattern of total score distribution and item responses were analyzed using graphical analysis and exponential regression model.
  
  
  RESULTS
  The total score distributions of the four subsamples exhibited an exponential pattern with similar rate parameters. The item responses of the K6 approximated a linear pattern from "a little of the time" to "all of the time" on log-normal scales, while "none of the time" response was not related to this exponential pattern.
  
  
  CONCLUSIONS
  The total score distribution and item responses of the K6 showed exponential patterns, consistent with other depressive symptom scales.
authors.affiliation: Department of Mental Health, Panasonic Health Center, Japan; Department of Drug Evaluation and Informatics, 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, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan; Department of Pharmacoepidemiology, Graduate School of Medicine and Public Health, Kyoto University, Kyoto, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Kawasaki
authors.affiliation: Department of Drug Evaluation and Informatics, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, 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.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Ide
authors.affiliation: Department of Drug Evaluation and Informatics, School of Pharmaceutical Sciences, University of Shizuoka , Shizuoka , Japan.
authors.forename: Maiko
authors.initials: M
authors.lastname: Akutagawa
authors.affiliation: Department of Drug Evaluation and Informatics, School of Pharmaceutical Sciences, University of Shizuoka , Shizuoka , Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.affiliation: Center for the Development of Cognitive Behavior Therapy Training , Tokyo , Japan.
authors.forename: Ono
authors.initials: O
authors.lastname: Yutaka
authors.affiliation: Department of Health Promotion and Human Behavior, Department of Clinical Epidemiology, Kyoto University Graduate School of Medicine, School of Public Health, Kyoto University , Kyoto , Japan.
authors.forename: Toshiaki A
authors.initials: TA
authors.lastname: Furukawa
keywords: CES-D; Depressive symptoms; Exponential distribution; General population; Item response theory; K6; Kessler screening scale; Latent trait; Likert scale; MIDUS