The psychometric validation of the Sheehan Disability Scale (SDS) in patients with bipolar disorder

Abstract

Bipolar disorder (BD) adversely affects daily activities/functioning. The Sheehan Disability Scale (SDS) assesses disability in work/school activities, family relationships, and social functioning, and it evaluates the functional impact of psychiatric disorders. BD outpatients from 21 U.S. sites completed a battery of validated instruments (including the SDS) three times over 8–12 weeks. Instrument reliability (internal consistency, test–retest), validity (construct, convergent validity, known groups) and responsiveness were measured. There were missing data for the SDS in 2% of the 225 subjects with BD. One factor explained 82% of the variance. All SDS items had rotated factor loadings on the first factor > 0.90, confirming the appropriateness of the SDS total score. Item-scale correlations surpassed 0.40. There was excellent internal consistency reliability for the SDS total score (Cronbach's alpha = 0.89). Test–retest reliability was acceptable for the SDS total score (intraclass correlation coefficient = 0.73). Correlations with other instruments demonstrate convergent and divergent validity. The SDS total and item scores significantly discriminated between (self-rated) overall health status, clinician-rated functional status, and clinician-rated depression, evidencing known group validity. The SDS demonstrated ability to detect change over time. The SDS is a valid, reliable measure of disability and is responsive to change over time when used in subjects with BD.