The Neurological Impairment Scale: reliability and validity as a predictor of functional outcome in neurorehabilitation

PURPOSE To examine the construct validity and inter-rater reliability of the Neurological Impairment Scale (NIS) and compare ratings by medical and multidisciplinary teams in a mixed neurorehabilitation sample. To assess its concurrent and predictive validity as a predictor of outcome and functional gains during inpatient rehabilitation. METHODS The NIS was rated in a consecutive cohort of patients (n = 428) recruited from nine specialist neurorehabilitation units in London. Dimensionality and internal consistency were explored through principal components analysis with Varimax rotation. Inter-rater reliability and the relationship between NIS and functional outcome (UK Functional Assessment Measure (FIM + FAM)) were analysed in a sub-sample (n = 94) from one centre. RESULTS Factor analysis identified two principal domains ("Physical" and "Cognitive") together accounting for 35% of the variance: their Cronbach's alpha values were 0.76 and 0.67, respectively. Inter-rater reliability was excellent for overall scores between doctors (ICC = 0.95 (95% CI = 0.91-0.97)) and acceptable between the medical and multidisciplinary team (ICC = 0.92 (95% CI = 0.88-0.95)). Change in NIS-physical score predicted 29% of the variance in functional gain (FIM + FAM change). CONCLUSION These findings provide the first formal evidence for the validity and reliability of the NIS as a measure of neurological impairment for use in general neuro-rehabilitation settings. Its further application and exploration are now warranted. IMPLICATIONS FOR REHABILITATION The extent of neurological recovery occurring during rehabilitation can make an important contribution to functional gains. In order to interpret measurement of functional outcome, we need to be able to identify changes at the level of impairment. Many of the available tools to measure severity of impairment are condition specific. The Neurological Impairment Scale (NIS) was developed for use across a broad range of disabling conditions alongside the UK FIM+FAM. This first formal examination of its psychometric properties provides evidence for its scalability, reliability and validity. The NIS has potential to provide useful information for case-mix adjustment and as a predictor of functional gain in general neurorehabilitation settings.