title: A hierarchy of distress and invariant item ordering in the General Health Questionnaire-12.
abstract: BACKGROUND
  Invariant item ordering (IIO) is defined as the extent to which items have the same ordering (in terms of item difficulty/severity - i.e. demonstrating whether items are difficult [rare] or less difficult [common]) for each respondent who completes a scale. IIO is therefore crucial for establishing a scale hierarchy that is replicable across samples, but no research has demonstrated IIO in scales of psychological distress. We aimed to determine if a hierarchy of distress with IIO exists in a large general population sample who completed a scale measuring distress.
  
  
  METHODS
  Data from 4107 participants who completed the 12-item General Health Questionnaire (GHQ-12) from the Northern Ireland Health and Social Wellbeing Survey 2005-6 were analysed. Mokken scaling was used to determine the dimensionality and hierarchy of the GHQ-12, and items were investigated for IIO.
  
  
  RESULTS
  All items of the GHQ-12 formed a single, strong unidimensional scale (H=0.58). IIO was found for six of the 12 items (H-trans=0.55), and these symptoms reflected the following hierarchy: anhedonia, concentration, participation, coping, decision-making and worthlessness.
  
  
  CONCLUSIONS
  The cross-sectional analysis needs replication.
  
  
  CONCLUSIONS
  The GHQ-12 showed a hierarchy of distress, but IIO is only demonstrated for six of the items, and the scale could therefore be shortened. Adopting brief, hierarchical scales with IIO may be beneficial in both clinical and research contexts.
authors.affiliation: Division of Population Health Sciences (Psychology), Royal College of Surgeons in Ireland, 123 St Stephen's Green, Dublin 2, Ireland. fdoyle4@csi.ie
authors.forename: F
authors.initials: F
authors.lastname: Doyle
authors.forename: R
authors.initials: R
authors.lastname: Watson
authors.forename: K
authors.initials: K
authors.lastname: Morgan
authors.forename: O
authors.initials: O
authors.lastname: McBride
mesh_terms: D000223:Adaptation, Psychological; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011581:Psychological Tests / Q000592:standards*; D013315:Stress, Psychological / Q000175:diagnosis*; D011795:Surveys and Questionnaires / Q000592:standards*