> Controlgroup? I don't think science means what you think it means.
In human studies, the absence of a control group invalidates the result. This is human studies 101.
As to science meaning what I think it does:
http://arachnoid.com/building_science
> That is scientific enough.
Spoken like a true psychologist. Observational studies without an effort to craft a testable, falsifiable theory, an explanation, for the observations is not science. If this were not so, astrology would be a science.
But since I can anticipate your reply, let me give you an example. Doctor Dubious invents a new treatment for the common cold. His treatment is to shake a dried gourd over the cold sufferer until the patient gets better. Sometimes the treatment takes a week, but it always works — the cold sufferer always recovers. So, why doesn't Doctor Dubious get a Nobel Prize for his breakthrough?
The answer is that the procedure is only a description — shake the gourd, patient recovers — without an explanation, without a basis for actually learning anything or being truthful about the connection between cause and effect. It's the same with psychology.
> What kind of evidence do you need for a "clear conclusion", if you don't accept decades of research, involving hundreds of thousands, if not millions of cases?
One study with a control group and scientific discipline, would be worth thousands of typical psychology studies that don't try to move from description to testable, falsifiable explanation. As it happens, the NIMH has now accepted this view. In a recent policy change, the NIMH has ruled that the DSM, psychology and psychiatry's "bible", may no longer be accepted as the basis for scientific research proposals, on the ground that it has no scientific content:
http://news.sciencemag.org/2013/05/nimh-wont-follow-psychiat...
But, since you think that the quantity of studies make up for their poor quality, will you also defend the many thousands of recovered memory cases on the same ground -- that, since there were so many of them, surely they must refer to something real? And that therefore Beth Rutherford really was raped by her father and forced to abort using a coat hanger -- until the day someone discovered she was a virgin?
Or how about Asperger Syndrome? A few years ago it seemed like a real thing, with thousands of confirmed diagnoses (for those of you who think counting cases makes up for poor discipline). Now, because of indiscipline and widespread abuse, it's been voted out of the DSM and therapists are discouraged from using it.
> There are even successful treatments for it.
Yes, just as there is for the common cold -- see above. If you actually understood science you would realize that ADHD means precisely nothing until a cause is uncovered.
> ADHD has been established as a syndrome, and about as firmly as it gets in medicine.
Compared to a microscope image of a pathogen, followed by development of a vaccine, which either succeeds or fails, in a properly designed study with a control group?
ADHD is located in the vast terrain of unscientific psychology, grouped with things that are discussed but for which there is no solid evidence nor known cause. The NIMH has taken the first step by denying use of the DSM in scientific research. The next step will be advances in neuroscience and the eventual replacement of psychology with neuroscience.
This doesn't say there's nothing to ADHD, or that a real cause might not eventually be uncovered. It says psychologists have no idea what they're talking about.