Lists that segment people into clearly-defined categories are particularly valuable to direct marketers, which can tailor their sales pitch to a particular demographic and therefore increase the likelihood of making a sale.

For instance, American Express offers bonuses such as free discount calling cards in its mailings to encourage students to sign up. Those perks might not appeal as much to the U.S. population at large.

So far, the ASL and ESL strategy for getting direct mail to college students has paid off.

"For the most part, our company, as well as most companies that market to the college student market, use American Student List," says Mendi Smith, the corporate communications director for Associates National Bank, one of the largest credit card providers in the country.

Getting Listed

Both ASL and ELS are extremely guarded about the manner in which they compile their databases and would not speak with The Crimson about the source of their student information.

ELS is a privately-held company and does not have to disclose any information about its business practices.

But ASL, which is owned by a publicly traded company, must file quarterly reports with the SEC.