TF and attention deficit-hyperactivity disorder: Meta-analysis demonstrated that there was no significant difference in serum transferrin level between the children with (n = 89, mean age = 8.2, mean female proportion = 36.3%) and without ADHD (n = 90, mean age = 8.2, mean female proportion = 38.1%)35,36 (k = 3, Hedges’ g = −0.324, 95% CI = −0.704 to 0.057, p = 0.096) (Fig. 2C).