A Rasch and confirmatory factor analysis of the General Health Questionnaire (GHQ) - 12

Smith, A., Fallowfield, L, Stark, D, Velikova, G and Jenkins, V (2010) A Rasch and confirmatory factor analysis of the General Health Questionnaire (GHQ) - 12. Health and Quality of Life Outcomes, 8 (45). ISSN 1477-7525

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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 six-item 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.

Item Type: Article
Keywords: EMTREE medical terms: adult; age; anxiety; article; cancer patient; controlled study; depression; factorial analysis; female; gender; General Health
Schools and Departments: Brighton and Sussex Medical School > Sussex Health Outcomes Research & Education in Cancer (SHORE-C)
Subjects: R Medicine > R Medicine (General)
Depositing User: Tracy Woodcock
Date Deposited: 26 Jul 2010
Last Modified: 30 Nov 2012 16:54
URI: http://sro.sussex.ac.uk/id/eprint/2446
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