> Just as a null result in Swedes[1] and Danes[2] demonstrates there is no effect, at least at the level of highschool. Why would that demonstrate there is no

> Just as a null result in Swedes[1] and Danes[2] demonstrates there is no effect, at least at the level of highschool. Why would that demonstrate there is no effect? No treatment -> no effect bolsters the case for education, as my example shows treatment -> effect. There was no change in education that would have led to large IQ increases during that period in those countries. There was in South Korea, and the effect on IQ was dramatic.