Study shows student attitudes toward free speech

> A fifth of undergrads now say it’s acceptable to use physical force to silence a speaker who makes “offensive and hurtful statements.”

> Results based on online survey of 1,500 undergraduate students at U.S. four-year colleges and universities, all U.S. citizens, conducted Aug. 17-31.

That's pretty scary and surprising. But for reference/context it would be great to know how different this is over time or how different it is from the general US population. Is it just the case that university attendance is rising and the student attitude is shifting to match the general population's attitude?