The second issue is that very few Web sites have sufficiently large numbers of visitors to compete with mass media outlets such as radio or television. Although a few Web sites have succeeded in attracting the large general audience that major advertisers have traditionally wanted to reach, most successful advertising on the Web is targeted at specific groups. The set of characteristics that marketers use to group visitors is called demographic information, which includes things such as address, age, gender, income level, type of job held, hobbies, and religion. It can be difficult to determine whether a given Web site is attracting a specific market segment unless that site collects demographic information from its visitors-information that visitors often are reluctant to provide because of privacy concerns.