science

16 points, so about a standard deviation. That's big, but your own varience can be just as high; the original point of IQ is a measure of how well you'll do in school to detect who may need additional attention (and not an inherent intelligence) so later aged tests include more on knowledge base while earlier tests are more about things like pattern recognition, mental rotation, etc. Infact, it has to get recurved regularly as each generation tends to be roughly 10 or 15 points higher (although idk about gen Z).

All this is to say that a slump of 16 points doesn't have to be shit like lead poisoning or gas fumes (although that certainly doesn't help, and pollution matters), it can simply be the US education system isn't good at teaching students. Cross culture studies already show that, as do differences between the rich and the poor. Or hell, just playing Tetris raises IQ, lol.

It'd obviously help if this wasn't a click bait article, though. People wanting to know why need to read a lot of actual research to know the myriad of different things that impact IQ and not just "haha US stupid."