Where do people come from before they arrive at these top news sites?
Nielsen gathers its data for this measure through the URL addresses that link a visitor to the news site. For example, if a user searched for news about Egypt through Yahoo and then from the search results clicked on a story from the BBC.com, the referral site would be Yahoo. On the other hand, if a user has a site like NYTimes.com as his or her main home page or types in the URL of the New York Times, no referral site exists.
To be counted as a referral site in Nielsen calculations, a site needs to meet a fairly minimal threshold.  Even then, the list of referring sites is not large—only 10-15 URLs emerge per site. That would suggest that the list of established guides to the Web, at least for news, has already narrowed to a handful of players.
In addition, the portion of traffic most of these places send to a site is small. Just three sites ever account for more than 10% of the traffic to any one site: Google (search and news combined), the Drudge Report and Yahoo (search and news combined). The remaining referral sites tend to account for less than three percent. In all, then, the referral sites make up 35-40% of a news site’s traffic.
Where does the remaining 60% of traffic to the top news sites come from? While Nielsen does not break down this specific percentage further, it does confirm that three behaviors make up the mix. First, people go to a site directly. That a user has that page as his or her home page, or types in the URL address itself. Second, a user can be referred to one page on a news site from a different page on that same domain—the sought-after self-referral. For example, a user reading a story on Examiner.com about local college graduates’ employment rates then clicks on an earlier story elsewhere on the site—thereby staying longer and diving deeper into the domain. Third, hundreds of sites, according to Nielsen’s estimates, send between one and four individuals to a site over the course of a month and thus are not named specifically.
1. For each month, Nielsen combines matching URLS and records those that have referred at least 5 individuals to a news site. In addition, a person is only counted once for each referring site. In other words, if one unique visitor came to CNN via Google three times in March, for example, that behavior would get counted once.
3. There are two exceptions here. Google News and Yahoo News have much higher referral percentages – namely from their sibling search components. Google Search refers about 60% of the traffic to Google News, and Yahoo search refers about 60% to Yahoo News.