nielsen_rentrakThe Wall Street Journal attempts to bring some clarity to the difference between Nielsen and Rentrak.

FOX’s announcement it was adding Rentrak to its 18 owned stations Wednesday may have left some wondering if Nielsen was on its way out.

WSJ reports, for now, the difference between the two may be as simple as national versus local.

Nielsen, which has long been the industry leader for TV research, still provides the ratings currency upon which national TV advertising is bought and sold. Nielsen collects that data through surveys of a sample of U.S. homes.

But broadcasters, which have complained that Nielsen’s numbers understate their true ratings, can use the deals with Rentrak to put pressure on Nielsen. Typically when broadcasters hire Rentrak they also keep using Nielsen. In the case of Fox Television Stations, an insider says it struck its deal with Rentrak as it negotiates a new contract with Nielsen, but say one has nothing to do with the other. Read more