title: Validation of the Rasch-based Depression Screening in a large scale German general population sample.
abstract: BACKGROUND
  The study aimed at presenting normative data for both parallel forms of the "Rasch-based Depression Screening (DESC)", to examine its Rasch model conformity and convergent and divergent validity based on a representative sample of the German general population.
  
  
  METHODS
  The sample was selected with the assistance of a demographic consulting company applying a face to face interview (N = 2509; mean age = 49.4, SD = 18.2; 55.8% women). Adherence to Rasch model assumptions was determined with analysis of Rasch model fit (infit and outfit), unidimensionality, local independence (principal component factor analysis of the residuals, PCFAR) and differential item functioning (DIF) with regard to participants' age and gender. Norm values were calculated. Convergent and divergent validity was determined through intercorrelations with the depression and anxiety subscales of the Hospital Anxiety and Depression Scale (HADS-D and HADS-A).
  
  
  RESULTS
  Fit statistics were below critical values (< 1.3). There were no signs of DIF. The PCFAR revealed that the Rasch dimension "depression" explained 68.5% (DESC-I) and 69.3% (DESC-II) of the variance, respectively which suggests unidimensionality and local independence of the DESC. Correlations with HADS-D were rDESC-I = .61 and rDESC-II = .60, whereas correlations with HADS-A were rDESC-I = .62 and rDESC-II = .60.
  
  
  CONCLUSIONS
  This study provided further support for the psychometric quality of the DESC. Both forms of the DESC adhered to Rasch model assumptions and showed intercorrelations with HADS subscales that are in line with the literature. The presented normative data offer important advancements for the interpretation of the questionnaire scores and enhance its usefulness for clinical and research applications.
authors.affiliation: Institute of Medical Psychology and Medical Sociology, University Hospital of RWTH Aachen, Pauwelsstraße 30, 52074 Aachen, Germany. tforkmann@ukaachen.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Forkmann
authors.forename: Maren
authors.initials: M
authors.lastname: Boecker
authors.forename: Markus
authors.initials: M
authors.lastname: Wirtz
authors.forename: Heide
authors.initials: H
authors.lastname: Glaesmer
authors.forename: Elmar
authors.initials: E
authors.lastname: Brähler
authors.forename: Christine
authors.initials: C
authors.lastname: Norra
authors.forename: Siegfried
authors.initials: S
authors.lastname: Gauggel
mesh_terms: D000328:Adult; D003866:Depressive Disorder / Q000175:diagnosis*; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires