FIG. 2.

Distribution of (a) ages and (b) admission Glasgow Coma Scale (GCS) scores in the study population. Both patient age and admission GCS scores demonstrated significant variability. Although slightly over half of the admission GCS scores were in the mild head injury range (GCS 13–15), significant numbers of cases in the moderate and severe head injury categories were included. Principal component analysis (PCA) is based partly on the recognition that predictors without substantial variability are less likely to account for differences in the observed outcome measure.