Investigating the shared factor structure of the GAD-7 and PHQ-9 in non-clinical samples of young adults

The Generalized Anxiety Disorder Scale-7 (GAD-7) and the Patient Health Questionnaire-9 (PHQ-9) are widely used to assess symptoms of generalized anxiety and depression among young adults. Although they have been validated separately, in recent years, they tend to be used conjointly. However, their scores are often highly correlated, raising doubts on the adequacy of using them together. Accounting for the shared and specific variance of these scales through bifactor-ESEM may provide significant advantages. To test this proposition, we compared hierarchical (bifactor) and non-hierarchical factor solutions combining both measures across non-clinical samples of young adults (N = 2926; 76% female; M_age = 22.39, SD_age = 3.69). The bifactor-ESEM solution, including a global factor of internalizing distress and two specific factors of generalized anxiety and depression, showed better psychometric qualities and full measurement invariance across gender and samples. Moreover, this model revealed distinct pathways linking self-control and emotion regulation to unique features of anxiety and depression, supporting its conceptual and practical relevance. Overall, bifactor modeling provides the most valid representation of GAD-7 and PHQ-9 scales when used conjointly in non-clinical samples of young adults.