The Nielsen Company still dominates U.S. TV ratings, but a new force is emerging in viewer tracking -- set-top data. FourthWall Media Inc. announced Tuesday an expansion of its MassiveData TV viewer index. The database now covers 1.8 million cable set-tops and reaches 4.7 million cable viewers. Even though it only launched the index in mid-2012, the company claims MassiveData is already the "largest independent source of cable viewing data." FourthWall is using set-top data to match advertisers with relevant viewing audiences. It promotes the initial success of that approach by pointing (somewhat obliquely) to political media buys that performed well in the 2012 election year. But FourthWall isn't the only company getting in on the TV data action. TiVo Inc.'s Research and Analytics unit (TRA), which tracks set-top data from 48,000 TiVo households, recently announced that it is combining that information with "psychographic" data revealing viewer attitudes and purchasing intent. (See TiVo Goes 'Psychographic'.) Verizon has also expressed an interest in sourcing data from subscriber set-tops to set new content licensing fees. (See Virgin Plugs Concurrent Into Its Video CDN.) Historically, service providers have been squeamish about monitoring and analyzing set-top data. But that attitude is now shifting because of the growing influence of Web-based marketing and advertising practices. What used to look like an invasion of privacy is increasingly becoming just a part of doing business in the digital age. — Mari Silbey, Special to Light Reading Cable