The development and initial validation of self-report measures of ICD-11 depressive episode and generalized anxiety disorder: The International Depression Questionnaire (IDQ) and the International Anxiety Questionnaire (IAQ).

BACKGROUND: The new International Classification of Diseases came into effect in 2022 (ICD-11; World Health Organization, 2022) and included updated descriptions and diagnostic rules for "Depressive Episode" and "Generalized Anxiety Disorder." No self-report measures align with these disorders so this study reports the development and initial validation of the "International Depression Questionnaire" (IDQ) and "International Anxiety Questionnaire" (IAQ). METHODS: Items were developed that aligned to the ICD-11 descriptions and their performance was assessed using data from a community sample (N = 2058) that was representative of the United Kingdom adult population. RESULTS: Item response theory models indicated that the two scales were unidimensional, and the items performed well in terms of difficulty and discrimination. Estimates of internal reliability were high. Based on ICD-11 derived diagnostic algorithms, 7.4% met requirements for ICD-11 Depressive Episode and 7.1% for Generalized Anxiety Disorder. CONCLUSIONS: The IDQ and the IAQ are short, easy to use, self-report measures aligned to the new and updated ICD-11 diagnostic descriptions. This study provides initial evidence that the scales produce scores that are reliable and valid.