The TV-ratings system in Turkey is in chaos following allegations that the identities of the 2,500 households equipped by Nielsen with people meters to collect viewing data were widely leaked across the industry.
Local production companies and TV stations have been accused of sending the viewers lavish gifts in order to distort the ratings data in their favor.
According to local media reports, six arrests were made at the end of last year, and police raided several production companies as well as Nielsen's local offices. It's not clear what happened to those arrested.
In a statement, Nielsen said that it had referred "an incident of data theft" to the police in September. "We are gratified to see the police pursuing its investigation," the statement said, adding that "Nielsen and its personnel are cooperating with the investigation."
The TV-buying system has since been in shambles. Without reliable new-audience measurement data, prices have been determined by using average ratings from the month before the scandal erupted, combined with monthly share performance from the whole of 2011.
The industry is working to regain media agencies' and advertisers' trust and is setting up a system slated to launch in May, in conjunction with Nielsen's rival TNS, part of WPP Group's Kantar research division.
The plan is to set up initially in just five cities with a sample of 1,040 households, according to Murat Yurddas, managing partner at Turkish media auditor Yurddas & Partners.
Martin Sambrook, international practice leader at media intelligence group Ebiquity, said, "It's a major embarrassment for Nielsen. The whole industry in Turkey must go out of its way to rebuild credibility. It's going to be a long slog."
However, the industry's response may not be robust enough to allay concerns. "The response of the industry bodies -- for both advertisers and agencies -- has been inadequate," Mr. Yurddas said. "They have all failed to come up with dependable, consistent and objective points of view during recent months."
Turkey's advertising association, RVD, said that only Turkish ratings body TIAK is allowed to discuss this issue. TIAK did not respond to e-mails requesting comment.
"We're not talking about a small country in the far-flung reaches of Asia or Africa," Mr. Sambrook said. "Increasingly, international media management is making decisions about where their funds should go, and if you can't have accountability, you can't invest."
Turkey, with a population of 70 million, is the second-biggest advertising market in Eastern Europe, after Russia. It ranks No. 16 of the 38 countries in the region of Europe, Middle East and Africa, according to Group M figures. Group M estimated that TV spending rose by 21% in 2011 and will grow by 13.9% this year, to $1.5 billion.
The country's two biggest advertisers are cell-phone operators Vodafone and Turkcell, which spent $93 million and $87 million, respectively, in 2010. They're followed by Unilever ($69 million) and Procter & Gamble ($66 million), according to Ad Age 's DataCenter.
