Purpose: The Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) assesses neurocognitive functioning in diagnosing sport-concussion. It includes low-score thresholds to detect poor effort or intentional underperformance to hide post-concussion impairments (“sandbagging”). However, individuals with Attention Deficit Hyperactivity Disorder (ADHD) often show lower ImPACT scores regardless of effort. Two previously proposed validity indices may better differentiate sandbagging from genuine poor performance.

Procedure: This study examines three seasons of baseline scores from 950 student-athletes. Rates of protocol invalidity produced by the traditional ImPACT indices and the external indices (Word-Memory Total Correct Distractors [WMTCD] and Design-Memory Total Correct Distractors [DMTCD]) were compared in athletes with and without ADHD using chi-squared tests.

Results: Athletes with ADHD did not perform worse than athletes without ADHD on either external index, F(2, 947)=0.98, p=0.91. The ImPACT validity indices flagged 3.4% of protocols as invalid, with a higher rate in athletes with (8.0% invalid) than without (2.9% invalid) ADHD, c²(1)=6.44, p2(1)=7.40, p2 (1)=3.47, p=0.06, though was not significantly different between athletes with (23.0%) and without (21.0%) ADHD, c²(1)=0.19, p=0.37.

Conclusions: External validity indices identified sub-optimal performance equally, suggesting they may aid in differentiating athletes performing at their best from those with naturally-occurring low baselines.