Development and testing psychometric properties of an ICF-based health measure: The Neuromuscular Disease Impact Profile

To develop a measure that is based on the International Classification of Functioning, Disability and Health (ICF) and reflects the prevalence and severity of disabilities related to neuromuscular disorders, and to evaluate the psychometric properties of this measure. A preliminary questionnaire was developed, based on the categories of the ICF Core Set for Neuromuscular Diseases. Next a cross-sectional postal survey was carried out among 702 patients (70% response rate) diagnosed with a neuromuscular disease. Finally, psychometric properties were examined. The preliminary Neuromuscular Disease Impact Profile (NMDIP) consisted of 45 items. Factor analysis showed that the NMDIP comprised domains representing 3 ICF-components: 5 factors in the Body Functions component, 2 factors in the Activities component, and 1 factor in the Participation component. Scales showed moderate to good internal consistency (α = 0.63-0.92) and mean inter-item correlation coefficients (0.38-0.77). Convergent and discriminant validity analysis indicated that the NMDIP measures the impact of neuromuscular disease on physical, mental, and social functioning. The NMDIP discriminates between groups who differ in extent of limitations. The NMDIP is an ICF-based measure that reflects neuromuscular disease-related disabilities. It consists of 36 items divided over 8 scales with satisfactory psychometric properties and 4 single items.