ADHD subtypes and neuropsychological performance in an adult sample

• Performance of ADHD and healthy adults on neuropsychological tests was compared.
• Effect sizes were largest between inattentive and combined ADHD subtypes.
• Whereas effect sizes between the two subtypes combined and controls were smallest.
• Differentiating ADHD adults from controls is poorest where subtypes differ most.

The study investigated, with an adult sample, the hypothesis that differences between subtypes of ADHD on neuropsychological tests contribute to the poor separation of ADHD and healthy groups on tests of this kind. Groups of ADHD inattentive (n = 16) and combined (n = 16) subtypes were carefully identified using DSM-IV criteria, and their performance on 14 measures of attention, memory, and executive function (EF) was compared between subtypes and between the two subtypes combined and a group of healthy controls (n = 30). Multivariate analyses showed statistically significant differences between the two subtypes, and between the two subtypes combined and the healthy controls. Importantly for the hypothesis, where differences for neuropsychological tests in terms of effect sizes between subtypes were largest, the differences in effect sizes between the two groups combined and controls were smallest (r = −0.64, 95% CI [−0.15, −0.87]).