Discriminant validity of the 12-item version of the general health questionnaire in a Swedish case-control study

Background: The 12-item version of the General Health Questionnaire (GHQ-12) is widely used as a proxy for Affective Disorders in public health surveys, although the cut-off points for distress vary considerably between studies. The agreement between the GHQ-12 score and having a clinical disorder in the study population is usually unknown.Aims: This study aimed to assess the criterion validity and to determine the sensitivity and specificity of the GHQ-12 in the Swedish population.Methods: This study used 556 patient cases surveyed in specialized psychiatric care outpatient age- and sex-matched with 556 controls from the Stockholm Health Survey. Criterion validity for two scoring methods of GHQ-12 was tested using Receiver Operating Characteristics (ROC) analyses with Area Under the Curve (AUC) as a measure of agreement. Reference standard was (1) specialized psychiatric care and (2) current depression, anxiety or adjustment disorder.Results: Both the Likert and Standard GHQ-12 scoring method discriminated excellently between individuals using specialized psychiatric services and healthy controls (Likert index AUC=0.86, GHQ index AUC=0.83), and between individuals with current disorder from healthy controls (Likert index AUC=0.90, GHQ index AUC=0.88). The best cut-off point for the GHQ index was 4 (sensitivity=81.7 and specificity=85.4), and for the Likert index 14 (sensitivity=85.5 and specificity=83.2).Conclusions: The GHQ-12 has excellent discriminant validity and is well suited as a non-specific measure of affective disorders in public mental health surveys.