When searching specifically for metrics used in diagnosis, some choice words come up from med central:

"A challenge with diagnosing ADHD is that the characteristics associated with the disorder – such as difficulties with focusing, shifting/dividing attention, managing frustration, organization/poor time-management, working memory, and staying engaged – are common symptoms that could have a breadth of etiologies.

As noted, *more often than not*, ADHD coincides with another disorder. "

Then for narrow-band symptoms will list examples of neuropsychological measures like D-KEFS, and finding details for each of these is again like pulling teeth. But looking at the description, all of what is tested could be impacted by other issues, including instability in home life, lifestyle factors, anxiety and depression, insomnia, etc