Yahoo had 17.2 million unique visitors aged 12 and older in the United States, RelevantKnowledge reported in its list of the top 25 Web sites.
Netscape drew 13.9 million visitors for the No. 2 spot, beating Microsoft's 13 million unique visitors.
RelevantKnowledge uses a representative panel of 7,000 home, business, and college Web users, which the company says can be projected to the universe of all Web users. The company also sells reports to Web sites and ad agencies with user demographics of site visitors, and it can create lists of most popular sites for particular age and demographic groups.
The service is designed to address complaints that because of the anonymous nature of Web surfing, no one really knows the demographic characteristics of who is visiting Web sites. Advertisers, and thus ad-supported Web sites, consider that information important for targeting particular demographic groups with ad banners.
RelevantKnowledge claims its service can break down demographics based on household income, region, household size, gender, age, location of use, professional status, and education level.