• by Joe Mandese  @mp_joemandese, December 21, 2007

At a time when the accuracy of Nielsen's metering systems are under acute scrutiny by the industry, the TV ratings researcher disclosed what is believed to be a rare failure in its supposedly fool-proof coding system, which is its backbone for measuring TV across digital platforms. The glitch, which was disclosed this week in a notice to clients, involved a failure of both the active and the passive components of Nielsen's system used to measure WKRN-TV, the ABC affiliate in Nashville, Tenn.

Nielsen did not explain to clients specifically what happened, but it acknowledged that the failure involved both the "station's encoding equipment" (the active portion of its system), as well as its Nielsen's passive monitoring of the station's signal.

Nielsen said the glitch happened twice: Once between Nov. 5 and Nov 7; as well as between July 10 and July 14. As a result, Nielsen said WKRN would be permitted to "retitle" its programming during those periods.

A Nielsen spokesman acknowledged that it is unusual to have both the encoding and the monitoring sites having problems at the same time, and that the redundancy in its so-called A/P system (active/passive) was designed to ensure things like that would not happen.

"The A/P system, with its dual ability to capture tuning, is an excellent way to measure TV viewing. Our goal is to ensure that the encoders and monitoring sites are working in tandem at their full capacity so that gaps remain rare," he said.

However, on Thursday, Nielsen issued a second client notice this week acknowledging that the Dec. 13th simulcast of the NFL feed of the Denver Broncos game on KWGN-TV, Denver, also "understated" the game's ratings due to "encoding issues."

"The Nielsen Company determined that a technical problem existed with the station's encoding equipment," Nielsen said. "Due to this encoding issue at the station, viewing to KWGN-TV's analog signal was credited to the NFL Network. This miscrediting resulted in an understatement of KWGN-TV's ratings and an overstatement of the NFL Network's ratings for the game." Nielsen said it still is assessing whether it is possible to determine what impact the KWGN glitch had on ratings, and that it would disclose those findings at a later time.