Equipercentile linking of the Sheehan Disability Scale and the World Health Organization Assessment Schedule 2.0 scales in people with mental disorders

Background: The Sheehan Disability Scale (SDS) and the World Health Organization Disability Assessment Scale (WHODAS 2.0) have been widely used to measure functional impairment and disability. To ensure that the scores from these two scales are practically exchangeable across diseases, therapies, and care programmes, the current study aimed to examine the linkage of the WHODAS 2.0 with the SDS and develop a simple and reliable conversion table for the two scales in people with mental disorders. Methods: A total of 798 patients (mean age = 36.1, SD = 12.7) were recruited from outpatient clinics of the Institute of Mental Health, and the Community Wellness Clinic in Singapore. Using a single -group design, an equipercentile equating method with log -linear smoothing was used to establish a conversion table from the SDS to the WHODAS 2.0 and vice versa. Results: The conversion table showed that the scores were consistent for the entire range of scores when the scores were converted either from the SDS to the WHODAS 2.0 or from the WHODAS 2.0 to the SDS. The agreement between the WHODAS 2.0's raw and converted scores and SDS's raw and converted scores were interpreted as good with intraclass correlation coefficient of 0.711 and 0.725, respectively. Conclusion: This study presents a simple and reliable method for converting the SDS scores to the WHODAS 2.0 scores and vice versa, enabling interchangeable use of data across these two disability measures.