Reliability and validity of the Portuguese version of the Generalized Anxiety Disorder (GAD-7) scale

Abstract

Background: Generalized anxiety disorder has a strong impact on health-related quality of life. For this reason, it seems relevant to develop strategies allowing early diagnoses in order to promote appropriate treatments. The objective of this study was to culturally adapt and validate the GAD-7 for the Portuguese patients with generalized anxiety disorder. Methods: For the cultural adaptation of the Portuguese version of the GAD-7 scale we started with a previous translation made by Mapi Institute and decided to perform a clinical review followed by a cognitive debriefing with patients. Once piloted, this version was then tested in a larger sample for feasibility and reliability (1-week test-retest). Construct validity was assessed by the relationship between GAD-7 and socio-demographic and clinical variables. Its unidimensionality was tested by principal component factor analysis. Criterion validity was assessed by comparing GAD-7 scores with those obtained by HADS, and EQ-5D. STAI was mainly used as a screening indicator for patient inclusion. Results: GAD-7 was considered feasible with a mean completion time of 2.3 minutes and no major floor or ceiling effects. We found an excellent Cronbach's alpha internal consistency score (0.880) and the test-retest and interclass correlation coefficients were also very good. Regarding the construct validity, younger patients, those with higher education, employed and without anxiety symptoms revealed lower GAD-7 scores, meaning better health. The unidimensionality of GAD-7 index was also confirmed by principal component factor analysis. At last, GAD-7 was significantly correlated with other health outcome indices and the classification levels created by it and by HADS showed to be dependent. Conclusion: The excellent metric properties confirmed the cultural adaptation and validity of GAD-7 into Portuguese population, allowing the clinicians an early detection and treatment of these patients.