Increased intra-individual variability among individuals with ADHD: first evidence from numerosity judgment and verbal and quantitative reasoning.

Background: This article presents the results of two studies investigating increased intra-individual variability (IIV) in the performance of individuals with attention deficit hyperactivity disorder (ADHD), in two cognitive domains: numerosity judgments and quantitative and verbal reasoning.

Methods: Study 1, a pre-registered experiment, involved approximately 200 participants (42.66% female; mean age: 36.