You diagnose a disease by the symptoms, this goes for any disease or disorder. Problem is that there are not actual diseases here but rather groupings of sympto

You diagnose a disease by the symptoms, this goes for any disease or disorder. Problem is that there are not actual diseases here but rather groupings of symptoms (as you say, its not just for ADHD though) and that its a checklist which is filled out often based solely on verbal questions answered by a child. Another interesting thing to consider is that a lot of psychological disorders are culture bound (and therefor in my humble opinion irrelevant as groupings even for psychiatric purposes).