Steve Hasker, Nielsen President/Media Products and Ari Paparo, Nielsen EVP/Online Products, disclosed in a letter 11/4 to clients that the company has been undercounting time spent traffic to websites for the last three months due to a flaw in its system. The glitch especially affected social media site numbers.
Nielsen is still investigating both the cause and extent of the error, which affects Nielsen’s NetView service, but likely also VideoCensus, MegaView Retail, MegaView Search, AdRelevance, WebRF services as well as custom research.
They’ve also asked the Media Rating Council to review the findings. Going forward, Nielsen will provide progress reports on its investigation, and advises clients to not use the data until the problems are fixed.
The letter said Nielsen’s systems were having problems with long URLs — more than 2,000 characters; sessions in which a visitor hit a page containing those long addresses simply weren’t counted. These long URLs have proliferated mostly due to social networks, like Facebook, which use URLs to pass data back and forth. However, this flaw would affect websites whether they used long URLs or not: If a Nielsen panelist visited one site with a long URL, all of the other web activity in the session was sometimes lost as well.
Nielsen believes this flaw has caused the appearance of a 22% decline in time spent on the web over the past several months. The company says the issue will be corrected for December data, which will be delivered in January.
Nielsen data isn’t used as buying currency, like its TV ratings, but it is used by agencies to plan spending and allocate dollars.