International Depression Questionnaire and International Anxiety Questionnaire: validation of brief ICD-11 measures...

The 11th revision of the International Classification of Diseases (ICD-11) introduced revised diagnostic criteria for a depressive episode (DE) and generalised anxiety disorder (GAD). The International Depression Questionnaire (IDQ) and the International Anxiety Questionnaire (IAQ) are the first self-report measures developed to assess and screen these disorders according to the ICD-11 diagnostic rules.

This study aims to validate the IDQ and the IAQ in clinical and community samples, examining internal consistency, factorial validity and construct validity.

The cross-sectional, observational multicentre validation study applied internal consistency testing, confirmatory factor analyses and item response theory (IRT) in a clinical sample (n=569; age 18-73; 417 females, 118 males, 34 diverse) and a sample representative of the German general population (n=1001) by age, education and gender (500 females, 499 males, 2 diverse). Factorial and IRT model fit of the IDQ and IAQ as well as concordance with the Patient Health Questionnaire-9 (PHQ-9) and the Generalised Anxiety Disorder-7 (GAD-7) was tested.

Both questionnaires showed excellent internal consistency (ω=0.96 each) and strong factor loadings. A three-factor IDQ model and a one-factor IAQ model provided the best fit. In the clinical sample, 39.7% met ICD-11 DE criteria and 51.0% GAD criteria (overlap 32.2%). In the general population, prevalence was 5.9% for DE and 9.3% for GAD. Concordance with PHQ-9 and GAD-7 was partial, suggesting differences between ICD-11-based and established screening tools.

The IDQ and IAQ are psychometrically robust self-report measures for ICD-11 DE and GAD. They are reliable, valid, brief, easy to administer, cost-free and suitable for use in primary care and research across diverse clinical and research settings. Their availability supports standardised screening of depression and GAD in both clinical and community settings.