Really though, I'm only focusing on your statement that there is are "large structural brain differences" in people with ADHD. I do not believe you are correct. I find no evidence for that in the primary literature, and what I've found basically says that any structural differences, if it does exist, must be small. Your responses also suggest that you haven't read the primary literature, nor understand the difficulties in interpreting the primary literature. (Which is entirely reasonable - it's not an easy skill to learn.)

As I pointed out in my earlier response, science journalism does a poor job of communicating science. Even the primary journals are subject to publication bias and other factors, which has lead to articles like "Why Most Published Research Findings Are False" http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1182327/ . If your information comes primarily filtered through science journalism and an occasional primary reference, then you may have an overly skewed view of the research results.

Based in what you've just written, you confirm by implication that there aren't large brain differences. If there were large differences, then ADHD would have a well characterized physical diagnosis. As you point out, it doesn't. It depends on psychological tests. You mention those tests take "multiple days and cost thousands of dollars to administer." But NMR or MRI scans do not take that much time nor cost that much, and would pick out "large structural brain differences", which tells me that there are no large structural brain differences that can be used as a diagnostic test for ADHD.

Then you mention 'the entire "ADHD isn't real" crowd'. I empathize with your frustrations, but that is a different topic. I am not a member of that crowd, nor was the primary reference which started this HN discussion saying that ADHD isn't real. Its argument is that ADHD is very likely overdiagnosed:

> Only one significant study has ever been done to try to determine how many kids have been misdiagnosed with ADHD, and it was done more than twenty years ago. It was led by Peter Jensen, now the vice-chair for psychiatry and psychology research at the Mayo Clinic, but at the time a researcher for the National Institute of Mental Health. After a study of 1,285 children, Jensen estimated that even way back then—...—between 20 and 25 percent were misdiagnosed. They had been told they had the disorder when in fact they did not.

It agrees with your statement that there are "variety of diagnostic criteria", and emphatically agrees with your earlier statement that "a 30 minute patient interview should not be the sole determining factor." It's horrible if someone isn't diagnosed as ADHD who would do better under ADHD treatment. It point is that it's also horrible if someone is misdiagnosed as ADHD and gets ADHD treatment even if it that treatment doesn't help, likely makes things worse by not getting the right treatment.

BTW, I looked for information about your [0]. See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3028268/ , "Bipolar and ADHD Comorbidity: Both Artifact and Outgrowth of Shared Mechanisms" (2010).

> Published rates of comorbidity between pediatric bipolar disorder (PBD) and attention-deficit/hyperactivity disorder (ADHD) have been higher than would be expected if they were independent conditions, but also dramatically different across different studies. This review examines processes that could artificially create the appearance of comorbidity or substantially bias estimates of the ADHD-BPD comorbidity rate ...

(The point is that if there are dramatically different results, then that may be because of artificial biases, rather than real ones.)

See also http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3201827/ , "Pediatric bipolar spectrum disorder and ADHD: comparison and comorbidity in the LAMS clinical sample" (2012)

> "Of 707 children, 538 had ADHD, 162 had BPSD, 117 had both ADHD and BPSD, and 124 had neither. Comorbidity (16.5%) was slightly less than expected by chance (17.5%). ... The high rate of BPSD in ADHD reported by some authors may be better explained as a high rate of both disorders in child outpatient settings rather than ADHD being a risk factor for BPSD." (italics are mine)

The limited search I did of the primary literature does not seem to give the same conclusion as what you have stated. While I don't know the literature, nor the field, I will be so bold as to suggest that things you believe to be true about ADHD are actually not so well understood as you believe them to be.