[MBCook]

But isn't that a problem? Shouldn't we try to split ADHD up into smaller more specific disorders so that we can better study/treat it?

If lumped all together, that seems to only help cause over-diagnosis (because the symptom list is so large) and makes it harder to study (because two very different conditions may be manifesting in very similar ways).

[spacedmountain]

Actually, it is split. There are three types of ADHD - predominantly hyperactive-impulsive (PH), predominantly inattentive (PI), and combined (C). There is also Sluggish Cognitive Tempo, which seems to be related to ADHD-PI, but there is less research on it.

Additionally, people who may seem to have ADHD may in fact have OCD, anxiety, depression, or other disorders. And vice versa. Or they may have a combination of one or more of these with ADHD.

[MBCook]

I was not aware of that.

As someone outside all of this (I've never had to deal with it, so I only have a passing familiarity) it sounds like the term ADHD needs to be removed from use as it's only causing more confusion. The various facets should have their own name.