"Nielsen Wednesday [Sept. 21, 2011] began informing clients about a major snafu … that generates gross ratings points (GRPs) for the multibillion [dollar] television advertising marketplace," reports Joe Mandese at MediaPost.
Mandese continues: "Nielsen said the glitch has been generating incorrect data for most of this year for GRPs and the reach and frequency estimates used as the basis for most TV advertising plans. Nielsen said the problem is under investigation, but some agency executives already believe it could lead to big problems with their TV audience guarantees that could result in millions of dollars in ‘make-goods’ from television networks."
The problem, basically, is that Nielsen seems to have been overstating DVR usage in its ratings since Jan. 31, 2011. Says the article, "Nielsen’s so-called C3 ratings, which include time-shifted viewing for three days after a program and its advertising have aired, is the official currency for the national TV advertising marketplace, and the basis for most TV advertising buys and audience guarantees."
The article adds that Brad Adgate, the head of research at independent media agency Horizon Media, "said the system where the new TV ratings problem occurred, Nielsen’s NPower platform, is what most advertisers and agencies use to get their reach and frequency and GRP, or gross rating point, estimates for their advertising buys and guarantees, as well as their ‘post buy analyses’ for evaluating their performance."