• by Joe Mandese  @mp_joemandese, December 2, 2011

Nielsen has begun informing clients of yet another significant data processing glitch – one that has been overstating estimates since 2007, the longest misstatement of Nielsen data disclosed to date. Nielsen executives say the data that was impacted – the sum of so-called ‘non-HUT” viewing sources – is rarely used by clients, but the fact that it took Nielsen so long to uncover the problem, and coming on the heels of other recent high-profile data glitches, raises serious questions about the researcher’s quality controls.

Nielsen executives say all the data for individual non-HUT viewing sources – which include viewing done on DVD players, DVRs, VCRs and videogame console systems connected to a TV set – have been processed accurately to date, but that the software that “aggregated” all of those sources into non-HUT viewing totals included a “faulty script” that double-counted and overstated the data in two of Nielsen’s major reporting systems: Npower and MarketBreaks.

In a notice sent to clients, Nielsen said none of its most important ratings data – including all program or “C3” ratings have been affected by the glitch, and that it is developing a timeline for correcting the faulty non-HUT viewing sources data in its databases.

Nielsen executives emphasized that the non-HUT totals have no practical impact on the TV programming or advertising marketplace, and are only a measure of how consumers are using those devices connected to TV sets. They say none of the viewing of “over-the-top” TV or online programming viewed on videogame consoles connected to TVs, for example, is currently factored into TV ratings, though that behavior is generally considered to be growing. During a recent industry conference CBS research chief Dave Poltrack equated viewing to one over-the top viewing source – Netflix – to currently being equivalent to the rating of a major cable television network.

The non-HUT data processing glitch disclosure comes only a couple of months after Nielsen informed clients that it had overstated nearly eight months of “frequency” data in its Npower system. While that glitch also did not affect Nielsen’s “currency” ratings – the ones used by advertisers and agencies as the basis of their TV advertising buys – the disclosure was embarrassing to Nielsen, especially because it was uncovered not by Nielsen’s analysts and technicians, but by clients who brought it to Nielsen’s attention.

While Nielsen executives say the new data glitch disclosure has little or no impact on the marketplace, some clients say it is unsettling and confusing at the very least and that it merits further investigation, including a “root cause analysis,” better disclosure, including a plan to avoid similar situations in the future, and possibly a response from the Media Rating Council, which is responsible for auditing and accrediting the systems that generated the faulty data.