I was diagnosed with ADHD, and while these criteria might have led to the testing, the actual testing was relatively scientific. There was a several hour battery of tests where my scores were compared against average. Most of the tests were relatively boring, like a computer screen would show letters, and you were supposed to hit the space bar for every character except Xs. People with ADHD performance at that task degrades much more quickly over time vs people without. There were also tests where people would employ different memory strategies to do them, and people with ADHD tend to use particularly poor ones. The doctor would read a list of 12 words, and you were supposed to recite it back. Then he'd tell you what words you missed, and you'd try to say the whole list again. Most people can get the whole list in 3-4 tries.

They also did an IQ test and the scores on all the ADHD tests were compared to what would be expected for my IQ. I performed at sub tenth percentile on many memory tasks, but my IQ was substantially hire than tenth percentile.