The General Health Questionnaire: a psychometric analysis using latent trait theory

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Abstract
This study examines the Likert-style successive integer scoring of Goldberg's (1972, 1978) General Health Questionnaire (GHQ) with a psychometric model in which the thresholds between successive categories within each item can be estimated. The model is particularly appropriate because the scoring of the successive categories, which are not named in the same way across items, by successive integers has received substantial discussion in the literature. Results from 1967 teachers in Western Australia who completed the 30-item form of the GHQ show that the items conform reasonably well to the model at a general or macro-level of analysis. In particular, the original ordering of categories is supported. However, as expected, there are systematic differences between distances among threshold within items and systematic differences among thresholds between items. The differences between positively and negatively orientated items confirm a suggestion in the literature that these two classes of items form sufficiently different scales so that they could be treated as separate, though reasonably correlated, scales.