In response to recent ratings irregularities, Nielsen conducted an extensive internal investigation of our systems and processes. On Oct. 6, 2014, we uncovered a technical error that impacts national network television ratings over several months.

The technical error was introduced on March 2, 2014, and was generally imperceptible until we saw high viewing levels associated with fall season premiere week. As a result, small amounts of viewing for some national broadcast networks and syndicators were misattributed. Cable networks and local TV ratings were not affected by this error.

A software fix to correct the problem was deployed on Oct. 9, 2014, meaning that all data being released today and going forward is correct.

In addition,

All of the commercial data-including C3-for the current TV season, which will begin releasing this weekend, will be correct. All previously released data since September 22nd will be reprocessed and reissued by Oct. 17, 2014. We will also reprocess all of the impacted data going back to Aug. 18, 2014, when the first new season broadcast network program aired. This data will be reissued by Oct. 31, 2014. Nielsen is also conducting an impact analysis to determine whether additional weeks should be reprocessed. We will work closely with our clients and the industry to provide updates as soon as possible. This issue has to do with difficult-to-attribute content called "all other tuning with code" (AOT with code). This data represents between 0.1% and 0.25% of all viewing minutes that we credit nationally. In the vast majority of cases, the impact is small; in a handful of cases, the impact is more significant.

As part of our investigation, we have also determined that there are no issues with the National People Meter, our data collection process, our panel, our TV audience measurement methodology or the total TV viewership data produced during this affected period.

We are working closely with our clients to manage this situation and will continue to be transparent with the industry and the media about our plans. In addition, we will undertake an exhaustive post-mortem-internally and with our clients-and we are asking Ernst & Young and the MRC to join us in these efforts.

Nielsen is committed to upholding the highest standards of television audience measurement and data processing, in order to provide the most effective audience measurement solutions to meet client needs.