The validity of the 12-item General Health Questionnaire in Australia: a comparison between three scoring methods

Objective: To investigate the specificity and sensitivity of three differen t scoring methods of the 12-item General Health Questionnaire (GHQ-12) and hence to determine the best GHQ-12 threshold score for the detection of men tal illness in community settings in Australia. Method: Secondary data analysis of the 1997 Australian National Survey of H ealth and Wellbeing (n = 10 641), using the Composite International Diagnos tic Interview as the gold standard for diagnosis of mental illness. Results: The area under the Receiver Operating Characteristic (ROC) curve f or the C-GHQ scoring method was 0.84 (95% CI = 0.83-0.86) compared with the area for the standard scoring method of 0.78 (95% CI = 0.76-0.80). The bes t threshold with C-GHQ was 3/4, with sensitivity 82.9% (95% CI = 80.2-85.5% ) and specificity 69.0% (95% CI = 68.6-69.4%). The best threshold score wit h the standard scoring method was 0/1, with sensitivity 75.4% (95% CI = 72. 5-78.4%) and specificity 69.9% (95% CI = 69.5-70.3%). These were also the b est thresholds for a subsample of the population who had consulted a health practitioner in the previous 4 weeks. Conclusion: In the Australian setting, the C-GHQ scoring method is preferab le to the standard method of scoring the GHQ-12. In Australia the GHQ-12 ap pears to be a less useful instrument for detecting mental illness than in m any other countries.