Reliability of the National Institutes of Health Stroke Scale

Abstract

Background and Purpose The reliability of the National Institutes of Health Stroke Scale (NIHSS) has been established through testing its use in live and videotaped patients. This reliability testing has primarily focused on the use of the scale by neurologists. We sought to determine the reliability of the NIHSS as used by non-neurologists in the context of a clinical trial. Methods In anticipation of the initiation of a randomized trial of a new therapy for patients with acute ischemic stroke, 30 physician investigators (30% of whom were not neurologists) and 29 non-physician study coordinators were trained in the use of the NIHSS at an informational and training conference using standardized videotaped patient examinations. A series of 4 patients were rated initially. After 3 months, the same 4 patients were rerated, providing a measure of intraobserver reliability. An additional series of 4 new patients were also rated after 3 months and, with the initial 4 ratings, provided data for assessment of interobserver reliability. Results Overall, 28% of the raters had previous experience with the NIHSS, and 22% had previously used the videotapes as used in the present trial. The coefficients of determination ( r 2 ) were each greater than .95 when the means of the two ratings of the same 4 cases were compared between (1) neurologists and other types of physicians, (2) physicians and study coordinators, (3) raters who had prior experience with the NIHSS and those without prior experience, and (4) raters who had used the videotapes in the past and those who had never viewed the tapes. The calculated r 2 s were greater than .98 for the initial rating of the first 4 cases and for the later rating of the 4 new cases. The slopes of the regression lines were all near 1, indicating that the raters were similarly calibrated. The intraclass correlation coefficients were .93 and .95, reflecting high levels of intraobserver and interobserver reliability. Conclusions These data extend the previously demonstrated reliability of the NIHSS to non-neurologists and show that both a variety of physician investigators and nurse study coordinators can be rapidly trained to reliably apply the scale in the context of an actual clinical trial.