As noted in a "UBS Online Education Sourcebook" published this month,  the "addressable" market for prospective higher education online learners in the U.S. totals about 17 million people, aged 25 to 44, who earn between $35,000 and $75,000, are married with children, work full time, and have access to the Internet.

UBS is a global financial services firm that provides investment banking, capital markets and wealth management products and services. The sourcebook is read primarily by people who have a business relationship with UBS.

UBS estimates that only 4 percent of the addressable market is being served by online educators, and they forecast a 25-30% five-year "purely online" revenue Compound Annual Growth Rate.

It was also noted that while the for-profits have proven to be the most aggressive players in the online learning marketplace, investors should not count out public institutions as "potential competitors."