Right, if your situation is just "X is the IQ cutoff for getting into college," you could infer that as more people go to college, X gets lower. But you could a

Right, if your situation is just "X is the IQ cutoff for getting into college," you could infer that as more people go to college, X gets lower. But you could also see a situation in which smart people opt out of college, so even if the number of people who wanted to go to school were constant, the average IQ would drop -- e.g. fifty years ago a smart person could succeed by getting a scholarship to a great school; now said person gets 90% of what he needs to know from Wikipedia, and can spread a great idea by uploading something to Sourceforge rather than muddling through the thesis-writing, thesis-approving process. I don't think it's just one phenomenon, and a model that either considers America a pure IQ meritocracy or assumes that college's role has changed by degree and not kind is clearly inadequate.