"They do worst then grads of previous generation though"
Again, selection bias. Currently everyone except a limited few are encouraged to go to college therefore the effect of selection bias has weakened over time and current grads don't do as well as grads of generations past.
This is simply selection bias or survivorship bias:
https://en.wikipedia.org/wiki/Selection_bias
"They do worst then grads of previous generation though"
Again, selection bias. Currently everyone except a limited few are encouraged to go to college therefore the effect of selection bias has weakened over time and current grads don't do as well as grads of generations past.