Not to mention that ADHD can't be diagnosed in the same manner as, say, a broken bone since it is (to make a simplification) a bunch of behaviors that suggest t

Not to mention that ADHD can't be diagnosed in the same manner as, say, a broken bone since it is (to make a simplification) a bunch of behaviors that suggest that maybe this individual's dopamine response is flatter than normal, sometimes aided in diagnosis with motor / memory tests. I would guess that this would make it difficult to control for misdiagnosis, and I would also guess that there are a fair number of misdiagnosed kids with ADHD seeing as about 2/3 of them "grow out" of it last time I checked. (Note: I have ADHD. It was obvious as a kid, but I wasn't diagnosed until I was 24 due to my parents religiosity. I know there are valid childhood diagnoses, and that we've made quite a lot of progress with understanding and being able to diagnose neuropsychiatric disorders. There also seem to be quite a few "social pressure" and "fad" diagnoses of ADHD in the USA -- if this study wants to be taken seriously, they might consider repeating it in other countries.)