A Two-Factor Theory for Concussion Assessment Using ImPACT: Memory and Speed

We present the initial validation of a two-factor structure of Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) using ImPACT composite scores and document the reliability and validity of this factor structure. Factor analyses were conducted for baseline (N 21,537) and post-concussion (N 560) data, yielding Memory (Verbal and Visual) and Speed (Visual Motor Speed and Reaction Time) Factors; inclusion of Total Symptom Scores resulted in a third discrete factor. Speed and Memory z-scores were calculated, and testretest reliability (using intra-class correlation coefficients) at 1 month (0.88/0.81), 1 year (0.85/0.75), and 2 years (0.76/0.74) were higher than published data using Composite scores. Speed and Memory scores yielded 89 sensitivity and 70 specificity, which was higher than composites (80/62) and comparable with subscales (91/69). This emergent two-factor structure has improved testretest reliability with no loss of sensitivity/specificity and may improve understanding and interpretability of ImPACT test results.