Figure 5B illustrates that the positive ion model accepted both R2 and Q2. Eight hundred fifty-six positive ion metabolites were found in the positive ion model; of these, 26 were considerably up-regulated (p < 0.05, VIP > 1) in ADHD compared to HCs, and 10 were significantly down-regulated (p < 0.05, VIP > 1), as shown in Figure 5C. Here, VIP is linked to attention deficit-hyperactivity disorder.