ebook_ADHD2019

The World Federation of ADHD Guide 27 time variability. 72 Slower and more variable reaction times are robust markers of ADHD not only compared to typically developing controls but also to individu- als with autism. 73 Last, but not least, it is frequently reported that children with ADHD have on average a lower IQ (about 9 scale points) than controls. 74 This reduction appears to be attenuated in adults with ADHD and is not fully caused by inattentiveness during test performance. This lower IQ may not be specific for ADHD and be found in individuals with other psychiatric disorders as well and might reflect executive deficits that are are assessed as part of the IQ battery tests. THE AVERAGE INDIVIDUAL WITH ADHD VERSUS INTERINDIVIDUALVARIATION All of the above described ADHD case-control cognitive differences were based on group effects. These group effects report on the “average” individual with ADHD but may disguise substantial interindividual variation. 75 Although most in- dividuals with ADHD show deficits in one or two cognitive domains, about 10-25 % have not any cognitive deficit with the test batteries used, and at the other side of the spectrum, only very few show deficits in all cognitive domains 34 . It is further of note that also 10% or more of all healthy controls (without ADHD) present with cognitive deficits in 2-3 domains. 34 This has led to attempts to identify sub- groups of ADHD with a more homogenous cognitive profile. One study revealed four cognitive subtypes, the first characterized by high response variability, the second by low performance on memory, inhibition and response speed, the third by inaccurate temporal information processing, and the fourth by sub-optimal arousal. Remarkably, very similar cognitive subgroups were found in a community sample of control children 33 . This supports the view that at least part of ADHD’s cognitive heterogeneity is nested within normal variation. Similarly, van Hulst and coworkers 76 identified three neuropsychological subgroups within children with ADHD: a quick and accurate, a slow and variable timing and a poor cognitive control subgroup. The first two of these subgroups were also present in the control Link in this https://www.youtube.com/ watch?v=4r3XWj269_g