Nielsen//NetRatings, a global Internet audience measurement and research company, said yesterday it will monitor visitor volume to China's four largest portals to get more detailed information of the surfers.

　　Nielsen//NetRatings will install its SiteCensus measurement tool onto every Web page of NetEase.com Inc, Sina Corp, Sohu.com Inc and Tom.com.

　　Each click on the pages will be recorded in the company's database, while the firm will also conduct off-line sample research to get the detailed information of the visitors, such as their sex, age, income and profession.

　　The financial details of the deal were not disclosed.

　　"Nielsen//NetRatings has more than 700 clients in the world including the global Internet giants MSN by Microsoft Corp, Yahoo! Inc and America Online Inc," said Hans Yu, Nielsen//NetRatings China's executive director. "Accurate data is a key driver for the growth of Chinese Internet firms and we can provide that service."

　　Sun Yan, a marketing executive at NetEase, said the company previously used data from the Internet Society of China for free before signing a contract with Nielsen//NetRatings.

　　Zhou Lei, an analyst at Internet business consultant Shanghai IResearch Corporation Limited, said:"Nielsen//NetRatings' measurement is more advanced than that of CNNIC (China Internet Network Information Center), given Nielsen's worldwide network and rich experience in the field."

　　"Comparatively, CNNIC's report only gives a vague picture of the Chinese Internet industry. Besides, its government-backed pedigree limits its worldwide influence," she said.

　　Zhou also noted the deal with Nielsen//NetRatings is a signal that Chinese Websites want to be international players on the global stage and want to gain the trust of the world community.Currently, Sina, Sohu and NetEase are listed on Nasdaq and Tom is going to sell its shares for the first time on Nasdaq next year.

　　China's Internet population is expected to reach 78 million people by the end of this year, Hu Qiheng, the chairwoman of the Internet Society of China, said at an Internet conference in Beijing over the weekend.

　　Nielsen//NetRatings started a trial service several months ago. The result suggested that some Chinese Websites may be listed among the world's top 20 in terms of visitors' volume.

　　But the company declined to reveal the result.