The psychometric validation of the Sheehan Disability Scale (SDS) in patients with bipolar disorder
Introduction
Bipolar disorder (BD) is a mood disorder characterized by recurrent episodes of mania and depression. Six different types of BD have been classified in DSM-IV (American Psychiatric Association, 1994), each varying in relation to the intensity and duration of manic and depressive episodes. Most common are the subtypes BD I (mania and major depression) and BD II (hypomania and major depression). The prevalence of BD is reported to be 3.7% (Hirschfeld, 2003).
The symptoms of BD have been shown to adversely affect daily activities, performance at work or school, and involvement in social activities (Calabrese et al., 2003). Disability or functional impairment is a concept that reflects the impact of the symptoms of a disease on a person's ability to conduct daily activities and fulfill social and familial roles (Hambrick et al., 2004). Disability is incorporated into the diagnostic criteria of most psychiatric disorders (American Psychiatric Association, 1994). In 1990, the World Health Organization identified BD as the sixth leading cause of disability-adjusted life years among individuals aged 15–44 years (Calabrese et al., 2003).
Systematic assessment of the patient's perspective can provide valuable information that can be lost when that perspective is filtered through a clinician's evaluation of the patient's response to clinical interview questions (US Food and Drug Administration, 2006). The Sheehan Disability Scale (SDS) is commonly used as a brief self-report measure of symptom-related disability (Sheehan, 1983).
The SDS was developed as a global measure of the impact of mental illness on functioning (Sheehan, 1983). The SDS is a composite of three self-rated, 10-point Likert scale response items that aim to assess the level of the subjects' impairment with regard to their work/school activities, family relationships, and social functioning. In addition, the numbers of lost and unproductive days due to symptoms are reported in two single items not included in the total score.
The SDS has been used in numerous psychiatric disorders including panic disorder, general anxiety disorder (GAD), major depressive disorder, BD, obsessive–compulsive disorder, and drug and alcohol dependence (Leon et al., 1992, Olfson et al., 1996, Sheehan et al., 1996). The validity and reliability of the SDS has been demonstrated in subjects with panic disorder (Leon et al., 1992) and social anxiety disorder (SAD) (Hambrick et al., 2004). The scale has been demonstrated to be discriminative of primary care subjects differing in impairment for depression, BD, specific phobias, GAD, substance abuse, and SAD (Olfson et al., 1996, Olfson et al., 1997, Hambrick et al., 2004).
An elevated Sheehan score (≥ 5) has been shown to be associated with an increased risk of psychiatric impairment (Leon et al., 1997). There is also evidence that the SDS is sensitive to change due to treatment, with 39.6% to 43.9% improvements in item scores for panic disorder subjects, and 28.9% to 35.2% improvements in scores for social phobia (Sheehan et al., 1996).
Despite its widespread use, the psychometric properties (including validity, reliability, and ability to detect change) of the SDS have not been assessed in subjects with BD. Neither has the performance of the instrument in different BD mood states been examined. The current study was undertaken with the intention of documenting the psychometric properties of the SDS as a measure of functional impairment in subjects with BD, and to provide information to assist researchers and practitioners in interpreting SDS scores in this population.
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Subjects
All subjects gave written, informed consent before entering the study, which was conducted according to the principles of the 1996 amendment of the Declaration of Helsinki and approved by Copernicus (a centralized ethics committee in the United States). Subjects were eligible for participation if they were at least 18 years of age; met the DSM-IV criteria for bipolar disorder I or II; were currently undergoing treatment for bipolar disorder as an outpatient; had no change in treatment in the
Subjects
In total, 226 subjects met the selection criteria completed questionnaires, and of these, 225 were included in the cross-sectional sample (one subject was excluded because he missed the family life/home responsibilities item of the SDS questionnaire). The test–retest sample consisted of 204 subjects who had useable SDS questionnaires at baseline and visit two, and 192 subjects were included in the responsiveness sample. Factor analysis and scaling tests were performed on the 222 subjects who
Discussion
Overall, the results suggest that the SDS has strong validity, reliability, and ability to detect change in subjects with BD. Mean baseline SDS item scores for subjects included in this study were higher (indicating more severe disability) than those reported previously for subjects with panic disorder (Leon et al., 1992) and similar to those reported previously for subjects with social phobia (Sheehan et al., 1996). Similarly, the mean baseline SDS total score in our study (19.48 ± 8.13) was
Acknowledgments
The authors thank the subjects who participated in the study. We are also indebted to the following investigators for enrolling and rating the subjects: Adams WW, Ashan M, Berlowski D, Bishop G, Booker, Bougard C, Carman TL, D'souza B, Grochowski S, Gross P (Paganetti N), Gupta S, Harding H, Herrea G, Kopolow L, Lerfald S, Marsh J, Menendez M, Montero J, Roberts N, Sarkis S, Shores L, Summers T, Tarnow J, Vijapura A, and Webber-Lind B. Thanks must also go to Dr. David Sheehan, Linda Abetz,
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Current address: The Mayo Mood Clinic and Research Program, Genomic Expression and Neuropsychiatric Evaluation (GENE) Unit, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.