Post-truth is an adjective defined as "relating to or denoting circumstances in which objective facts are less influential in shaping public opinion than appeals to emotion and personal belief". I mean, post-truth is the way to define beliefs that people think which aren't proofed at all but because of the fact that everyone says it, everyone believes it and it's thought as a proofed theory or fact.
I can perfectly relate that to my own topic, the overdiagnosis in children. A way to associate this to my topic is talking about the existence or not about TDAH.
Years before, nobody had this disorder, just for the reason that nobody knew from its existence, it wasn't "invented" or "discovered" yet. Since the first psychiatrist came up with that idea, everyone started to comment it and nowadays, it's a common disorder to have, in my opinion, psychologists diagnose this disorder too much and too quickly.
I can also talk about the other hand of this theme, TDAH. More or less 20 years ago, everyone was diagnosed to have this disorder, it was like a craze. Nowadays it's also like a craze, but in reverse, at the moment lots of doctors are refusing the existence of this disease, so more and more people and doctors are starting to refuse it too. Based on lots of statistics, that happens because of the lack of knowledge people has about this disorder, if more people knew what is about, the consequencies and general information about it, more people would have their own opinion about this theme and won't base their thoughts on other people's ones.
So, I actually think it has led to the extreme, when lots of people start to believe something, more and more people believe it too. That's a dangerous fact, and more if the thought they extremely believe is about health, like in this case.
In my opinion, it's not true that it doesn't exist, because some people actually have it and it's so evident its existance. However, a big quantity of people that are diagnosed to have it, don't have this disorder, because of the fact that somebody has big difficulties to concentrate, doesn't mean at all that this person has to have TDAH.
There are more examples of post-truth related to overdiagnosis in children: the relationship between obesity and asthma, and lots more. But from my point of view, the existance or not of TDAH is a clear example of post-truth.