METHODOLOGIC ISSUES An overview of the injury severity score and the new injury severity score

Objective—The research was undertaken to describe the injury severity score (ISS) and the new injury severity score (NISS) and to illustrate their statistical properties. Design—Descriptive analysis and assessment of the distribution of these scales. Methods—Three data sources—the National Pediatric Trauma Registry; the Massachusetts Uniform Hospital Discharge Data Set; and a trauma registry from an urban level I trauma center in Massachusetts—were used to describe the distribution of the ISS and NISS among injured patients. Results—The ISS/NISS was found to have a positively skewed distribution and transformation did not improve their skewness. Conclusion—The findings suggest that for statistical or analytical purposes the ISS/ NISS should not be considered a continuous variable, particularly if ISS/NISS is treated as a continuous variable for correlation with an outcome measure. (Injury Prevention 2001;7:10–13)