Factorial invariance of a computerized version of the GAD-7 across various demographic groups and over time in primary care patients

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Background: The Generalized Anxiety Disorder 7-item scale (GAD-7) is commonly used by clinicians and researchers to screen for anxiety disorders and to monitor anxiety symptoms in primary care. However, findings regarding its factor structure are mixed, with most studies reporting a best-fitting for a one-factor structure, whereas others indicate a two-factor model. To be valid for comparisons, the GAD-7 should measure the same latent construct with the same structure across groups and over time. We aimed to examine the best-fit factor structure model of the GAD-7 among primary care patients and to evaluate its measurement invariance. Methods: A total of 1255 patients completed the computerized version of GAD-7 and a subsample of 238 cases was assessed at the 3-month follow-up. A confirmatory factor analysis (CFA) was performed and analyses of multiple-group invariance were also conducted to determine the extent to which the factor structure was comparable across various sociodemographic groups and over time. Results: The results showed that both a one- and two-factor structure (representing somatic and cognitive-affective components) were invariant across sociodemographic groups and over time. The two-factor structure provided the best model fit. Limitations: Results cannot be generalized to all primary care patients, as only patients whose general practitioners consider them to suffer emotional disorders were included. Conclusions: Our study supports the reliability and validity of the one- and two-factor model of the GAD-7, both for screening purposes and for monitoring response to treatment.