Factor structure, internal consistency and construct validity of the Sheehan Disability Scale in a Spanish primary care sample

Rationale, aims and objectives The Sheehan Disability Scale (SDS) is a three-item instrument that measures disability in three inter-related domains: work, family life/home responsibilities and social/leisure activities. The main objective of the present study was to examine the factor structure, reliability and construct validity of the SDS in a wide Spanish sample of primary care (PC) patients. Methods One phase cross-sectional survey. A total of 3815 patients, aged 18 years or older attending PC for a medical visit, were interviewed between October 2005 and March 2006. The interviews included the Structured Clinical Interview for DSM-IV Axis I Disorders for depressive and anxiety disorders, the Mini-International Neuropsychiatric Interview for the rest of mental disorders, a medical conditions checklist, the 2.0 version of the 12-item Short-Form Health Survey (SF-12) for measuring quality of life and the SDS. Results The principal component analysis and the subsequent confirmatory factor analysis indicated that the SDS is one-dimensional (normed fit index = 0.990, non-normed fit index = 0.987, comparative fit index = 0.991, goodness-of-fit index = 0.993, standardized root mean-square residual = 0.037, root mean-square error of approximation = 0.053). The internal consistency of the scale was good (alpha = 0.83) and it was significantly associated with the physical and mental component of the SF-12. Concerning discriminative validity, patients with major depression or panic disorder scored higher on the SDS than patients with chronic medical conditions or with no chronic pathology. We also found that a cut-off point of 8 in the SDS adequately discriminated between patients with and without depression (area under the curve = 0.814, sensitivity = 81.60%, specificity = 70.60%). Conclusions The SDS seems a reliable, valid and useful clinical tool for measuring disability in Spanish PC patients.