Development and validation of the NIMHANS-NMHS-2 disability scale (NNDS)

Measuring disability is one of the primary objectives of India's National Mental Health Survey-2 (NMHS-2). The survey required a scale that was short, free to use, culturally flexible, administrable by lay-interviewers, and measuring disability aligned with the current understanding of mental disorders.

Lacking a scale meeting these requisites, the NIMHANS-NMHS-2 Disability Scale (NNDS) was developed as a new adult disability scale. This manuscript reports on its development and validation.

Nineteen items across six domains were generated by desk review. Content validation conducted by 16 Consultants at the National Institute of Mental Health and Neuro Sciences led to removal of six items (Content Validity Index <0.75). Analysis included Cronbach's alpha for internal consistency and Exploratory Factor Analysis. K-means cluster analysis identified disability severity groups, while receiver operating characteristic analysis determined optimal disability cut-offs based on WHO-Disability Assessment Schedule (WHODAS) and NNDS scores.

The NNDS was validated across inpatient (n = 141) and Outpatient (n = 142) sample from NIMHANS, and a community sample (n = 133). It demonstrated excellent internal consistency (α-0.94), a stable five-factor structure, and strong correlations with the WHODAS 2.0 (rho = 0.93), and Brief Psychiatric Rating Scale (rho = 0.80). Cut-off scores established were: No disability: 13-17; Mild: 18-31; Moderate: 32-40, and Severe: >40.

The NNDS has demonstrated robust psychometric properties for measuring disability. Being open-source, the scale has broad applicability for clinical practice, community assessments and research. (For the NMHS-2, an eight-item short version is being used, its development and validation are separately submitted for consideration of publication).