If I remember correctly, researchers suspect that there was significantly decreased lead exposure around that time. I personally prefer to think of it as the Flynn Result rather than the Flynn Effect, because the second seems too much like the Flynn Cause. There are a bunch of reasons why measured IQs could increase, and some of them are there sometimes and not other times, and the measured increase fluctuates accordingly.
If true then why has it been acting on white Americans post 1960?
If I remember correctly, researchers suspect that there was significantly decreased lead exposure around that time. I personally prefer to think of it as the Flynn Result rather than the Flynn Effect, because the second seems too much like the Flynn Cause. There are a bunch of reasons why measured IQs could increase, and some of them are there sometimes and not other times, and the measured increase fluctuates accordingly.