Background and Objectives: Our study explored the validity of different threshold values on the 12-item version of the General Health Questionnaire (GHQ12) for estimating the prevalence of anxiety and mood disorders (AMD) in Ontario population survey data. Methods: Data were drawn from the 2003, 2004 and 2006 cycles of the CAMH Monitor (N = 7,126), an ongoing general population survey of Ontario adults aged 18 and older, which includes the GHQ12. The concordance of different threshold values on the GHQ12 for determination of AMD with a criterion based on individuals who were prescribed either anti-anxiety or anti-depressant drugs in the past 12 months and who reported 14 or more mentally unhealthy days in the past 30 days was examined using receiver operator characteristic (ROC) analysis. Results: Concordance between the GHQ12 determination of AMD and the criterion measure reached "moderate" levels. ROC analysis revealed an area under the curve (AUC) of 0.89. At a GHQ12 threshold value of 4, the specificity and sensitivity values obtained were 0.92 and 0.71, respectively. Also at that value, the estimated prevalence of AMD was nearly identical to that seen in recent Canadian studies using the CIDI. Conclusions: These analyses suggest that the GHQ12 may be suitable for providing a proxy measure of AMD for epidemiological and surveillance purposes. A threshold score of 4 seems to be most suitable for these purposes when using Canadian data.
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