The way that it is handled today, "ADHD" seems to represent a spectrum of symptoms rather than a well-understood root cause.
I've seen people go through school and adulthood, with different doctors vacillating between "you definitely have ADHD" and, "there is no chance that you have ADHD". Clearly something is up, and their symptoms broadly fit the guidelines, but the typical medication (amphetamines) sometimes seems to do more harm than good. "It helps me focus, but gives me no control over what I focus on" is a common refrain, even in this thread.
I am sure that accurate diagnoses have helped a lot of people, and I don't want to belittle that. Based on my personal experience, though, I'm not sure that "prevalence of ADHD" is a particularly useful label for large-scale analyses.
The prevalence of spectrum disorders being used as a catchall leads to over-diagnosis/mis-diagnosis. Many times there may be underlying causes that never or rarely get resolved or correctly diagnosed.
Chronic heavy metal poisoning for example was a common underlying cause that was often diagnosed as a spectrum disorder depending on symptoms presented.
It was very difficult to test because it doesn't stay in the blood but instead binds almost immediately. You had to work with a willing doctor and use a chelator and cause acute poisoning to determine if this was the case. Treatment options were not very good either.
For example, many people who received silver dental fillings have had this, while the ADA called it silver, and promoted it as stable, science in the last 20 years has shown marked neurotoxic effects which is why its mostly not used anymore (to my understanding).
The chemical composition of those fillings was 50% by weight mercury which leached when people drank acidic drinks (i.e. soda). Teens and young adults were at higher risk.
I've seen people go through school and adulthood, with different doctors vacillating between "you definitely have ADHD" and, "there is no chance that you have ADHD". Clearly something is up, and their symptoms broadly fit the guidelines, but the typical medication (amphetamines) sometimes seems to do more harm than good. "It helps me focus, but gives me no control over what I focus on" is a common refrain, even in this thread.
I am sure that accurate diagnoses have helped a lot of people, and I don't want to belittle that. Based on my personal experience, though, I'm not sure that "prevalence of ADHD" is a particularly useful label for large-scale analyses.