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

Abstract

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.

• Measure
• Neurological Impairment Scale
• outcome assessment
• psychometrics

Acknowledgements

The authors gratefully acknowledge the hard work of the clinical teams in the nine centres who collected the data and to the patients to whom it belongs.

Copies of the Neurological Impairment Scale are available free of charge from the corresponding author, or downloaded from our website http://www.csi.kcl.ac.uk/NIS.html.

Declarations of interest

This article presents independent research commissioned by the National Institute for Health Research in England (NIHR) under its Health Research Health Services and Delivery Research (NIHR HS&DR) programme (project number 08/1809/235) and its Programme Grants for Applied Research funding scheme (RP-PG-0407-10185). Please visit the NIHR website for more information. The views expressed in this article are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. Financial support for the preparation of this manuscript was also provided by the Dunhill Medical Trust, the Luff Foundation.

Outcome measurement is a specific research interest of our centre. The NIS and the UK FIM + FAM were both developed through this department, but are disseminated free of charge. None of the authors has any personal financial interests in the work undertaken or the findings reported.