The impact of ambiguous response categories on the factor structure of the GHQ-12

Previous research has suggested multiple factor structures for the 12-item General Health Questionnaire (GHQ-12), with contradictory evidence arising across different studies on the validity of these models. In the present research, it was hypothesized that these inconsistent findings were due to the interaction of 3 main methodological factors: ambiguous response categories in the negative items, multiple scoring schemes, and inappropriate estimation methods. Using confirmatory factor analysis with appropriate estimation methods and scores obtained from a large (n = 27,674) representative Spanish sample, we tested this hypothesis by evaluating the fit and predictive validities of 4 GHQ-12 factor models-unidimensional, Hankins' (2008a) response bias model, Andrich and Van Schoubroeck's (1989) 2-factor model, and Graetz's (1991) 3-factor model-across 3 scoring methods: standard, corrected, and Likert. In addition, the impact of method effects on the reliability of the global GHQ-12 scores was also evaluated. The combined results of this study support the view that the GHQ-12 is a unidimensional measure that contains spurious multidimensionality under certain scoring schemes (corrected and Likert) as a result of ambiguous response categories in the negative items. Therefore, it is suggested that the items be scored using the standard method and that only a global score be derived from the instrument.