My mentor, Leon Eisenberg, once commented that when we started out in the 1960's studying "hyperactive children" --now called ADHD--it was hard to convince anyone that they really existed or that it mattered. Especially doubtful were the British, led by their great scholar Michael Rutter. Now the schools and homes seem to be flooded by them, to the point of an epidemic. Although my old colleague Paul Wender, also at Hopkins in the 1960's, had first alleged that adults also had ADHD, nobody took that idea seriously until recently. Now there is a claim that their prevalence even exceeds the 2 to 3 percent of child ADHD, and over the last 5 years their prevalence has steadily and rapidly increased.
Recently the National Comorbidity Survey of the World Health Organization (WHO) under Harvard scholar, Ron Kessler, has placed the figure at 4 to 5 percent whereas the estimates for childhood ADHD average around 2 to 4 percent. What gives? Can there be more adult ADHD than child ADHD?
First, there are now dozens of studies throughout the world that consistently place childhood ADHD as high as 10 percent of the population, and averaging round 4 to 6 percent. Are there really 10 kids out of a hundred with ADHD (3 or 4 in every average classroom)?
Well how does one KNOW? Remember that these studies usually involve hundreds or thousands of children, so that defining a case cannot usually involve individual clinical interviews. Instead, they may involve telephone surveys, checklists of symptoms, or surveys of parents.
Remember too, that according to the standard psychiatric definition (the Diagnostic and Statistical Manual of the American Psychiatric Association, now in its 4th revision, called DSM-4), there are 5 criteria that must be met.
The most important of those criteria is the one that requires that the symptoms not be better explained by some other illness; that is, a "differential diagnosis" must be made. If it's autism, or depression, or anxiety, etc., then the 18 ADHD symptoms could be caused by one of these other illnesses.
But wait! Doesn't that mean you have to do a COMPLETE psychiatric examination? If you don't then the presumed "case" of ADHD could be something else, and the total count of ADHD cases would include all the other possible diagnostic contenders.
Now examining all of the epidemiological studies of ADHD, the only one that I know of that actually used a complete diagnostic interview on enough children to form a reliable prevalence estimate was a study by Adrian Angold and Jane Costello in the Western counties of North Carolina. Their prevalence rate for ADHD: less than 2 percent. Incidentally, they found that a great many children who did NOT meet ADHD criteria were being treated for it, and a great many who DID meet criteria were not being treated for it. Obviously a correct diagnosis is necessary to avoid both kinds of mistakes. Wow! ADHD IS BOTH UNDERESTIMATED AND OVERESTIMATED at the same time, and they are being unter-treated and over-treated at the same time.
Now what about the adults? The big problem here is that there are no agreed-upon criteria for adult ADHD, though there is much work being done to alter the criteria to account for developmental changes in symptomatology, age of onset, and types of impairment associated with the condition. DSM-V will undoubtedly give us the basis for a real epidemiologic survey.
However, the afore-mentioned WHO study started with a subsample of the very large survey carried out around the world, and by using statistical methods (e.g. imputing the actual numbers for the whole sample from a smaller subsample), they used 6 symptoms that were included in the original survey, to arrive at a prevalence estimate for adult ADHD, based on followup telephone interviews of the smaller subsample. The result: 4 to 6 percent prevalence of adult ADHD.
Here again, there really is no full psychiatric interview, so that in my mind these high figures must remain suspect. Incidentally, I am not reassured by the fact that this "WHO Study", which I participated in, was sponsored in part by a drug company, and that shortly after the first findings the drug company was using the 6 symptoms as a diagnostic guide for recommending adults to see their physician for possible treatment.
So here we have another possible explanation of the explosive growth of adult ADHD: it is a boon for pharmaceutical companies who are now virtually all scrambling to get FDA approval for ADHD drugs in children to be approved for adults as well.
Don't get me wrong; adult ADHD is a real problem, and one that can be successfully treated by medication and other methods, and is a condition that has serious consequences for the patient and their families. But if ADHD, as we and most scientists agree, is a developmental problem starting early in life, then it seems unlikely that the true prevalence for adults can be more than the prevalence for children.
Adults will pass through the age of risk for many other psychiatric and emotional conditions than is the case for children, so that they will have more comorbidities and more impact on their adult lives than they did as children. On the whole they could be sicker, though many compensate or adjust to their illness, especially those well-treated as children. But it is precisely these other conditions which might better explain their illness and dysfunctions, so they may be mis-diagnosed as ADHD when they are not ADHD cases at all, just as many children have likewise been mis-diagnosed because their symtoms could be due to other disorders that were not screened for.
The bottom line: SYMPTOMS ALONE CANNOT MAKE A TRUE DIAGNOSIS. It is a mistake to make the diagnosis without carefully ruling out other explanations. To do this requires a sound clinical interview by a trained mental health professional.