Objectives: The aim of the study was to validate a new case-finding instrument for common mental disorders (CMDQ).
Methods: A cross-sectional, stratified, two-phase study was carried out in 28 general practices in Aarhus County, Denmark. 1785 consecutive patients, 18-65 years old, consulting 38 GPs with a new health problem participated. Patients were screened before consultation using a one-page screening questionnaire including subscales for somatisation (SCL-SOM and Whiteley-7), anxiety (SCL-ANX4), depression (SCL-DEP6) and alcohol abuse (CAGE). A stratified subsample of 701 patients was interviewed using the Schedules for Clinical Assessment in Neuropsychiatry (SCAN) interview. We tested the external validity of the scales using the SCAN interview as gold standard. All data were analysed using appropriate weighted procedures to control for the two-phase sampling design and non-response bias.
Results: Estimates of sensitivity and specificity for relevant ICD-10 diagnoses at theoretical optimal cut-off points on subscales: Depressive disorder: 78/86 (SCL-DEP6); Alcohol abuse or dependence: 78/97 (CAGE); Severe anxiety disorder: 77/85 (SCL-ANX4); Somatisation disorder: 83/56 (SCL-SOM); and 75/52 (Whiteley-7); any mental disorder: 72/72 (SCL-8). At the theoretical optimal cut-off points the CMDQ demonstrated higher diagnostic accuracy than GPs on any diagnosis evaluated.
Conclusion: The study results suggest that the CMDQ has excellent external validity for use as a diagnostic aid in primary care settings.