This seems a fair and cogent observation ...... but wouldn't that just indicate that the issue has been a hidden problem.
You can't take out numbers for comparisons when you have such factors as "hidden problem", "demographics", "inconsistent research method over time" etc...
In order for such a research to be accurate, they would have to rent an isolated island with two camps with each holding at least 5000 people that have identical living conditions and identical medical history, and then keep them ther for 50 years with one camp giving each other blowjobs and the other one not.
As you see the basic problem with such an experiment is that it is inhumane. Therefore many researches that have something to do with social habits are very vague and besed more on deductive logic than any real observation and evidence. Psychology is especially infamous in this area (To clarify: Psychology is not accepted as "science" by the scientific community).
Basically I don't trust a research that has been very inconsistent in it's observation. A lot has changed in medical science since 1974, and people are way better diagnosed today, than they were before.
Just to prove my point: Do you think there are severely more people with ADHD today, than in 1974, or do you think diagnose method is much more effective?
Hmmmm do you know something about the research group or the funding of the research to back this up ....... at least the idea that the research is 'Agenda' driven ??
I would need the actual journal to find out who is funding them and eventually finding out about the organisation.... not hard, but very time consuming, so I will just use deductive reasoning that they are agenda driven because they overlooked very important factors. If you don't accept my reasoning, I will not blame you, because after all I question this research for the very same reason.