A Rasch and confirmatory factor analysis of the General Health Questionnaire (GHQ) - 12
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RESEARCH
A Rasch and confirmatory factor analysis of the General Health Questionnaire (GHQ) - 12 Research
Adam B Smith*1, Lesley J Fallowfield2, Dan P Stark3, Galina Velikova†3 and Valerie Jenkins†2
Abstract Background: The General Health Questionnaire (GHQ) - 12 was designed as a short questionnaire to assess psychiatric morbidity. Despite the fact that studies have suggested a number of competing multidimensional factor structures, it continues to be largely used as a unidimensional instrument. This may have an impact on the identification of psychiatric morbidity in target populations. The aim of this study was to explore the dimensionality of the GHQ-12 and to evaluate a number of alternative models for the instrument. Methods: The data were drawn from a large heterogeneous sample of cancer patients. The Partial Credit Model (Rasch) was applied to the 12-item GHQ. Item misfit (infit mean square ≥ 1.3) was identified, misfitting items removed and unidimensionality and differential item functioning (age, gender, and treatment aims) were assessed. The factor structures of the various alternative models proposed in the literature were explored and optimum model fit evaluated using Confirmatory Factor Analysis. Results: The Rasch analysis of the 12-item GHQ identified six misfitting items. Removal of these items produced a sixitem instrument which was not unidimensional. The Rasch analysis of an 8-item GHQ demonstrated two unidimensional structures corresponding to Anxiety/Depression and Social Dysfunction. No significant differential item functioning was observed by age, gender and treatment aims for the six- and eight-item GHQ. Two models competed for best fit from the confirmatory factor analysis, namely the GHQ-8 and Hankin's (2008) unidimensional model, however, the GHQ-8 produced the best overall fit statistics. Conclusions: The results are consistent with the evidence that the GHQ-12 is a multi-dimensional instrument. Use of the summated scores for the GHQ-12 could potentially lead to an incorrect assessment of patients' psychiatric morbidity. Further evaluation of the GHQ-12 with different target populations is warranted. Background The General Health Questionnaire belongs to a family of instruments for assessing psychiatric morbidity in both community and non-psychiatric settings [1]. The original General Health Questionnaire (GHQ) comprised 60 items and versions with fewer items have been developed from this, e.g. the GHQ - 30, GHQ - 28 and GHQ- 12 [1,2]. The GHQ -12 is a brief, well validated instrument [3], yet despite its brevity there has been considerable debate in the literature regarding the dimensionality of the instrument. Although originally intended as a unidimensional instrument, a number of exploratory and con* Correspondence: [email protected] 1 Centre for Health & Social Care, Charles Thackrah Building, University of Leeds,
UK Contributed equally
†
Full list of author information is available at the end of the article
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