How well defined is ADHD?

I’ve long had attention and focus problems, but never explored the possibility that I have ADHD till recently. I understand that it’s a standard term, but I’m still a bit suspicious; Psychiatry doesn’t seem like the most reliable field.

Are there good reasons for picking out the behaviors associated with ADHD and giving them a name? Obviously this is a different question than whether ADHD is a ‘disorder’ or ‘disease’, and whether ADHD medication is good or bad for people.

Answers that would satisfy me

  • Behaviors associated with ADHD strongly cluster

  • Analyzing questionnaires of attention and focus behaviors with faction analysis naturally produces an ‘ADHD dimension’ that explains a lot of variance (similar methodology to identifying Big 5 personality traits).

  • ADHD diagnosis a strong predictor of anything interesting (income or grades or some contrived but interesting lab test)?

  • Something else along these lines.