I understand ADHD is a standard term, but I'm still a bit suspicious that it's not a useful one; 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?

• Behaviors associated with ADHD strongly cluster
• Analyzing questionnaires of attention and focus behaviors with factor analysis naturally produces an 'ADHD dimension' that explains a lot of variance (similar methodology to identifying Big 5 personality traits).
• ADHD diagnosis is a strong independent predictor of something interesting: income or grades or some contrived but interesting lab test (controlling for obvious things like IQ)
• Something else along these lines.
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It's certainly fine to be dubious of such things, and I don't necessarily disagree with you, but it would make your question stronger if you had some sources to back up your initial claims. –  Chuck Sherrington Nov 16 '12 at 4:50
Except for my claim that ADHD is a standard term, everything else is based on vague impressions, so I think lack of sources gives my question the right amount of credibility. –  John Salvatier Nov 16 '12 at 16:14

Like all psychiatric disorers, ADD and ADHD are diagnosed using a set of criteria listed in the Diagnostic and Statistical Manual of Mental Disorders, or DSM

The latest version is the DSM-IV-TR. The DSM-V is due out in 2013 and may change these criteria.

Diagnosis is expected to be done by a licensed professional who is able to assess these criteria.

INATTENTION
(need 6 of 9)

- often fails to give close attention to details or makes careless mistakes in schoolwork, work or other activities
- often has difficulty sustaining attention in tasks or play activities
- often does not seem to listen when spoken to directly
- often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (no if oppositional behavior or doesn’t understand instructions)
- often has difficulty organizing tasks and activities
- often avoids, dislikes, or is reluctant to engage in tasks or activities that require sustained mental effort (such as schoolwork or homework)
- often loses things necessary for tasks or activities (e.g., toys, school assignments, pencils, books, or tools)
- often easily distracted by extraneous stimuli
- often forgetful in daily activities

HYPERACTIVITY-IMPULSIVITY
(need 6 of 9)

- often fidgets with hands or feet or squirms in seat
- often leaves seat in classroom or in other situations in which remaining seated is expected
- often runs about or climbs excessively in situations in which it is inappropriate (in adolescents or adults, may be limited to subjective feelings of restlessness)
- often has difficulty playing or engaging in leisure activities quietly
- is often "on the go" or often acts as if "driven by a motor"
- often talks excessively
- often blurts out answers before questions have been completed
- often has difficulty awaiting turn
- often interrupts or intrudes on others (e.g., butts into conversations or games)

REQUIREMENTS

- Present at least 6 months, maladaptive and inconsistent with development level
- Some symptoms that caused impairment were present before age 7
- Some impairment from the symptoms is present in two or more settings (e.g., at school {or work} and at home)
- There must be clear evidence of clinically significant impairment in social, academic or occupational functioning

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None of this answers the original question: Do these traits tend to cluster strongly? Is there reason to believe that they share an underlying etiology? etc. –  octern Nov 16 '12 at 21:15
The original question is "How well defined is ADD/ADHD?" The bit about traits clustering together is listed as a potential answer. There's also nothing in there about etiology. –  Jeff Nov 16 '12 at 21:19
You're right, my mistake. I was thinking about the other question in the post, "Are there good reasons for picking out the behaviors associated with ADHD and giving them a name?" –  octern Nov 17 '12 at 1:49
you're right though, that this isn't the best answer. it doesn't address how criteria for the DSM are chosen. my understanding is that this processes is subjective and controversial, but maybe someone can provide a more detailed explanation. –  Jeff Nov 17 '12 at 2:06