Internal Consistency Reliability, Construct Validity and Discriminative Validity of the Depression, Anxiety, Stress Scale-۲۱ (DASS-۲۱) in Iranian Patients with Multiple SclerosisRunning title: Internal Consistency Reliability, Construct Validity and Discriminative Validity of DASS-۲۱

Introduction: The evaluation and diagnosis of psychiatric symptoms in multiple sclerosis (MS) could play a prominent role in controlling and treating them. This study aimed to assess the internal consistency reliability, construct validity and discriminative validity of the Persian version of depression anxiety stress scales-۲۱ (DASS-۲۱) in patients with MS.Materials and Methods: In a cross‐sectional study in ۲۰۱۰, ۱۶۲ patients were selected by a consecutive method. DASS-۲۱ was evaluated for its reliability (by the internal consistency method), construct validity, and discriminative validity. In order to achieve this aim, the Fatigue Severity Scale (FSS) was used. Data were analyzed using Cronbach’s alpha coefficients, Pearson correlation coefficients, and multivariate analysis of covariance (MANCOVA).Results: Internal consistency for the subscales of depression (α=۰.۸۹), anxiety (α=۰.۸۲), stress (α=۰.۸۶), and the total DASS-۲۱ (α=۰.۹۴) score was excellent. The analysis of the validity of DASS-۲۱ showed that all the scale items had strong positive correlations with the subscales on their own (r=۰.۶۲ to ۰.۸۳). The mean of all DASS-۲۱ subscales was significantly greater in fatigued patients than that in non-fatigued patients (P<۰.۰۵).Conclusion: DASS-۲۱ shows good psychometric properties in a population of Iranian patients with MS and can be used in clinical settings and related research.

Keywords:

Validity and Reliability , Depression , Anxiety , Psychological Stress , Multiple Sclerosis