title: Factor structure and measurement invariance of the Patient Health Questionnaire-9 for female and male primary care patients with major depression in Germany.
abstract: BACKGROUND
  Depression is characterized by gender-specific distinctions, with women being affected more often than men. The Patient Health Questionnaire-9 (PHQ-9) is frequently used to assess depression in primary healthcare. Previous research has yielded heterogeneous findings on the factor structure, and little is known of its measurement invariance across gender. The aim of this study was 1) to evaluate the fit of four previously hypothesized models of PHQ-9 factor structure in patients with major depression in German family practices, and 2) to test the measurement invariance of the best-fitting model across gender.
  
  
  METHODS
  We used the baseline data from a cluster-randomized controlled trial. The diagnosis of major depression was based on the PHQ-9 and confirmed by the family physician. We calculated Confirmatory Factor Analyses (CFA) to assess which of the previously hypothesized factor structures (a one- and three different two-factor solutions) would best fit our data. We also calculated Complex Survey Analyses (CSA) and Multi Sample Analyses (MSA).
  
  
  RESULTS
  We included 626 participants (75.4% women and 24.6% men). A two-factor model with five 'somatic' labeled items and four 'non-somatic' labeled items presented the best fit indices. The model measurement was invariant across gender.
  
  
  CONCLUSIONS
  The inclusion criteria used in the main trial mean the study sample was not representative of all patients with major depression in German family practices.
  
  
  CONCLUSIONS
  The measurement invariance across gender revealed by this study is a precondition for the use of the PHQ-9 without gender-specific adaptation in patients with major depression in German family practices.
authors.affiliation: Institute of General Practice, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany. Electronic address: petersen@allgemeinmedizin.uni-frankfurt.de.
authors.forename: Juliana J
authors.initials: JJ
authors.lastname: Petersen
authors.affiliation: Institute of General Practice, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Paulitsch
authors.affiliation: Department of Educational Quality and Evaluation, German Institute for International Educational Research, Frankfurt am Main, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Hartig
authors.affiliation: Institute of General Practice, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Karola
authors.initials: K
authors.lastname: Mergenthal
authors.affiliation: Institute of General Practice, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany.
authors.forename: Ferdinand M
authors.initials: FM
authors.lastname: Gerlach
authors.affiliation: Institute of General Practice, Goethe-University Frankfurt am Main, Frankfurt am Main, Germany; Institute of General Practice, Friedrich Schiller University Hospital Jena, Jena, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Gensichen
mesh_terms: D000328:Adult; D003865:Major Depressive Disorder / Q000175:diagnosis*; D005163:Factor Analysis, Statistical; D005194:Family Practice; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D011320:Primary Health Care; D011569:Psychiatric Status Rating Scales; D011594:Psychometrics; D011795:Surveys and Questionnaires
keywords: Major depression; Primary healthcare; Psychiatric status rating scales (MESH terms)