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.
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.
The cross-sectional analysis needs replication.
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.