Using Hospital Anxiety and Depression Scale (HADS) on patients with epilepsy: Confirmatory factor analysis and Rasch models

Purpose: The problems of mood disorders are critical in people with epilepsy. Therefore, there is a need to validate a useful tool for the population. The Hospital Anxiety and Depression Scale (HADS) has been used on the population, and showed that it is a satisfactory screening tool. However, more evidence on its construct validity is needed. Method: A total of 1041 people with epilepsy were recruited in this study, and each completed the HADS. Confirmatory factor analysis (CFA) and Rasch analysis were used to understand the construct validity of the HADS. In addition, internal consistency was tested using Cronbachs' alpha, person separation reliability, and item separation reliability. Ordering of the response descriptors and the differential item functioning (DIF) were examined using the Rasch models. Results: The HADS showed that 553% of our participants had anxiety; 56.0% had depression based on its cutoffs. CFA and Rasch analyses both showed the satisfactory construct validity of the HADS; the internal consistency was also acceptable (alpha=0.82 in anxiety and 0.79 in depression; person separation reliability = 0.82 in anxiety and 0.73 in depression; item separation reliability = 0.98 in anxiety and 0.91 in depression). The difficulties of the four-point Likert scale used in the HADS were monotonically increased, which indicates no disordering response categories. No DIF items across male and female patients and across types of epilepsy were displayed in the HADS. Conclusions: The HADS has promising psychometric properties on construct validity in people with epilepsy. Moreover, the additive item score is supported for calculating the cutoff. (C) 2016 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.