An article in the Sacramento Bee† was titled "College freshmen show conservative side" and reported the results of a fall 1997 survey "based on responses from a representative sample of 252,082 full-time freshmen at 464 two- and four-year colleges and universities nationwide." The article did not explain how the schools or students were selected.
For this survey, explain what a unit is, what the population is, and what the sample is.