CONCLUSION: ApEn recognized the increased chaotic response in ADHD. This was confirmed by three effect sizes, AUC and p value during ROC analysis. Still, ApEn is an unreliable mathematical marker. ADHD discrimination was only achieved by extending the surveillance ranges for r; 0.8 → 1.0 and m; 1 → 3 at intervals of 0.0167. This necessitates an ‘a priori’ study making it inapt for online analysis. Even so, it could be useful in ‘post hoc’ analysis.