That wasn't the question.
The question wasn't "Why is it so over-diagnosed?" it was "Is it ACTUALLY over-diagnosed or is that just what people SAY it is?"
I'm fairly confident that ADHD doesn't effect 10% of the population (that's roughly how many American children the CDC says has been diagnosed with ADHD), although part of my argument revolves around the definition of a disorder.
To me, for it to count as a disorder, it would have to be intrinsic, AKA "your mind works this way" as opposed to "you act this way due to an external situation". The thing is, ADHD appears to be tied to location. Within the US, it becomes more common towards the east coast:
Prevalence of ADHD also appears to be tied to time, aka less adults appear to have ADHD than kids. And it seems to be a modern thing. If you look at mental states in the past that were decently common but weren't understood, such clinical depression, addiction, or paranoia, they still showed up in stories of the time, just not named as disorders. And those conditions (with the possible exception of addiction) affect way less than 10% of humans. ADHD doesn't seem, to me, to have the presence in fiction across the ages that it should if it affected 10% of the population. Although, granted, ADHD can be dismissed as laziness or general distractedness, but way less than 10% of characters in fiction are portrayed as distractable/lazy people.
So while I would agree ADHD is real, evidence suggests to me there is an external situation that produces ADHD like symptoms in those that do not actually have ADHD. Given that this situation appears to occur in a specific part of the US and mostly applies to school aged children, my conclusion is that kids who don't fit into the school system are incorrectly being diagnosed with ADHD.
Actually there are reports that ADHD is hereditary, they were just classed as unruly or slow learners before. And there a
plenty of accounts of lazy, stupid or unruly people in fiction.
It may be over-diagnosed. Most sources say 3-5%, not 10%. But that 3-5% is in England where they feed kids proper school meals, not hotdogs made of "pink slime" like the USA, if you're lucky to get a school meal at all. The diet in USA is absolutely horrendous, and probably is adding to all sorts of childhood problems.
I've read accounts by British child psychologists when kids are diagnosed the dads (it's much more prevalent in males) often go "that sounds like me when i was a kid, but I was just called
XYZ" (lazy, stupid, etc)
Then there's stuff like this, which I just found:
http://www.reuters.com/article/2010/09/30/us-adhd-genes-idUSTRE68S5UD20100930(Reuters) - British scientists have found the first direct evidence attention deficit/hyperactivity disorder (ADHD) is a genetic disorder and say their research could eventually lead to better treatments for the condition.
Researchers who scanned the gene maps of more than 1,400 children found that those with ADHD were more likely than others to have small chunks of their DNA duplicated or missing.
[...]
The study also showed an overlap between the deleted or duplicated DNA segments, known as copy number variants (CNVs), and genetic variants linked to the brain disorders autism and schizophrenia -- providing what the scientists said was "strong evidence" that ADHD is a neurodevelopmental condition.
And as for historical references, that's easy to look up:
http://en.wikipedia.org/wiki/History_of_attention_deficit_hyperactivity_disorderIn 1775, Melchior Adam Weikard, a prominent German physician and physician to the Russian Empress, Catherine II, published a medical textbook containing a chapter on attention deficits, now believed to be the first known reference to ADHD in the medical literature.
[...]
In his chapter on attention deficits, Weikard's description contains many of the symptoms now associated with the inattentive dimension of ADHD in the Diagnostic and Statistical Manual for Mental Disorders - 4th edition.