November 4, 2010, 4:09 PM

Nielsen discloses flaws in how it measures online traffic

The company blames long URLs for the problem.

Lead Photo

Audience measurement firm The Nielsen Co. today told its clients that its data for traffic to online sites is flawed. The company put most of the blame on its failure to properly account for long URLs, such as those used by shoppers when following links from a search engine to an online retail site. Nielsen said it expects to have fixed the problem in time for December reports, which will be released in January.

The problem has marred data for the Nielsen NetView service. The company says it is investigating the impact on Nielsen’s VideoCensus, MegaView Retail, MegaView Search, AdRelevance and Nielsen WebRF services, along with custom research products.  Nielsen suggests limited use of online audience measurement data until the company completes its investigation.

“The primary cause is an increasing incidence of web sites using very long URLs that are not properly recognized by our systems,” write Steve Hasker, president of media products, and Ari Paparo, executive vice president of online products, in a letter today to clients. “When our system attempts to process session data including the very long URLs, which are more than 2,000 bytes in size each, it intermittently does not recognize the session.” 

An executive from an online retailer who asked not to be named explained the problem: Consumers searching for a product via a search engine such as Google come across a product for sale at the online retailer’s e-commerce site. A consumer hovering over the link at Google can see, in the bottom of the browser, the type of long URL that has caused the problems at Nielsen. Clicking on the link will send the consumer to the relevant product page on the online retailer’s site, but Nielsen won’t necessarily be able to record that visit because of the long URL.

“They have under-reported our numbers horribly over the past year,” says the executive, whose company is among the top 50 retailers in the Internet Retailer Top 500 Guide. “They’ve not been able to absorb our links. It makes us look bad in the monthly updates from Nielsen.” The bad data also could harm a company’s value in the eyes of investors, the executive says.

The executive adds that the company has complained to Nielsen for the better part of a year that Nielsen data did not match the retailer’s internal site traffic data; the retailer employs at least one other vendor to measure online audiences.

In the letter to clients, Nielsen promised to issue bi-weekly progress reports on the investigation, starting next week. “The extraordinary changes and complexity of how the Internet is used warrants our increased attention to help the entire industry mature with a trusted source of data,” the letter says. “We sincerely apologize for these data issues and will work closely with you to rectify the situation.”

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