Validation of a Polish version of the National Institutes of Health Stroke Scale: Do moderate psychometric properties affect its clinical utility?

Abstract

Background: The National Institutes of Health Stroke Scale (NIHSS) is a validated tool for assessing the severity of stroke. It has been adapted into several languages; however, a Polish version with large-scale psychometric validation, including repeatability and separate assessments of anterior and posterior stroke, has not been developed. We aimed to adapt and validate a Polish version of the NIHSS (PL-NIHSS) while focusing on the psychometric properties and site of stroke.

Methods: The study included 225 patients with ischemic stroke (102 anterior and 123 posterior circulation stroke). Four NIHSS-certified researchers estimated stroke severity using the most appropriate scales to assess the psychometric properties (including internal consistency, homogeneity, scalability, and discriminatory power of individual items) and ultimately determine the reliability, repeatability, and validity of the PL-NIHSS.

Results: The PL-NIHSS achieved Cronbach's alpha coefficient of 0.6885, which indicates moderate internal consistency and homogeneity. Slightly more than half of the individual items provided sufficient discriminatory power (r > 0.3). A favorable coefficient of repeatability (0.6267; 95% confidence interval: 0.5737-0.6904), narrow limits of inter-rater agreement, and excellent intraclass correlation coefficients or weighted kappa values (> 0.90), demonstrated high reliability of PL-NIHSS. Highly significant correlations with other tools confirmed the validity and predictive value of the PL-NIHSS. In posterior stroke, the PL-NIHSS achieved the required Cronbach's alpha coefficient (0.71070). Additionally, stroke location did not affect other psychometric features or instrument reliability and validity.

Conclusions: We developed a valid and reliable tool for assessing stroke severity in Polish-speaking participants. Moderate psychometric features were emphasized without limiting its clinical applications.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Pictogram showing modified words, phrases, and pictures for better assessment of speech disorders, inattention, and extinction in a Polish-speaking population.

Fig 2. Bland–Altman diagram indicating the repeatability of the Polish version of the National Institutes of Health Stroke Scale (PL-NIHSS).

The distribution of plots is based on the mean and difference from the total PL-NIHSS scores obtained by two randomly selected examiners. The limits of agreement occupy the area between the dashed lines. The 95% confidence interval of the regression line is located between the orange bold lines.

Fig 3

Construct (A) and predictive (B, C) validity of the Polish version of the National Institutes of Health Stroke Scale (PL-NIHSS). Significant correlation with Glasgow Coma Scale (GCS) on the first day of stroke. Significant correlations with (B) modified Rankin Scale (mRS) and (C) Barthel index on the 90th day of stroke.