Psychometric Analysis Of The Generalized Anxiety Disorder Scale And The Patient Health Questionnaire Using Mokken Scaling And Confirmatory Factor Analysis

The Generalized Anxiety Disorder Scale (GAD-7) and Patient Health Questionnaire Depression Scale (PHQ-9) are widely used measures in primary health care used to assess anxiety and depression.While there is no doubt about their reliability and validity, there is some question over their factor structure.Many have suggested that both are one factor scales.However, there is some evidence that they can also be seen as having two subscales that correspond to a Cognitive/Affective aspect and a Somatic aspect.In this study the dimensional structure of both scales is examined using Mokken analysis which is an Item Response Theory approach, and also confirmatory factor analysis.The relationship of the scales two each other and also to the Work and Social Adjustment Scale (WSAS) is also investigated.There is evidence to support the idea of a Cognitive/Affective and Somatic subscale in both measures.While both measures are positively correlated with the WSAS, the PhQ-9 and indeed the PHQ-2, have significantly stronger relationships with it than the GAD-7.