• by Laurie Sullivan  @lauriesullivan, August 26, 2011

Facebook had 870 million unique visitors and 1 trillion unique page views in June, according to Google data. But some news sites and data firms now suggest the stats are inaccurate. The question becomes how much marketers should trust these stats when planning media buys.

The data compiled by Google's DoubleClick Ad Planner rankings are from "anonymized" Web traffic and aggregated Google Toolbar data and metrics. It allows marketers to see a monthly updated list for the largest 1,000 sites worldwide through the ad management service.

comScore suggests the stats are false. Its report for July found that Facebook had 467 billion monthly page views. In a CNN article, comScore Spokesperson Stephanie Flosi said "cookie-based methodologies will always have inflated numbers compared to panel-based, because people delete their cookies throughout the month. For a site with high engagement like Facebook, this is going to result in overstatement of figures."

Google admits on the site the numbers are approximate and should not be considered completely accurate.

Nonetheless, Google gives marketers a guideline by allowing them to click on the link for each of the companies listed in the 1,000 sites to discover demographics of site visitors, such as household income and age. For example, 24% of the site visitors in June were between the ages of 35 and 44; 22% between 25 and 34; and 22% between ages 45 and 54.

For each site on the list, marketers can see the site category, unique visitors, page views and whether the site has ads. The data provides ad placement information, specifications and keywords to find the site.

YouTube, the Google video Web site, grabbed the No. 2 spot with 790 million visitors, 100 billion page views and about a 42.6% reach of those online. Yahoo sites followed at No. 3 with 590 million visitors, 78 billion page views and a 31.8% online reach.

The Google data also lists other search engines. Live.com took No. 4 on the list with 540 million unique visitors, 59 billion page views and 29% reach of those online. Chinese search engine Baidu came in at No. 8 with 310 million unique visitors, 120 billion page views, and 16.4% reach.

Bing took the No. 11 spot with 230 million unique visitors, more than 9 billion unique page views, and 12.4% reach. Ask came in at No. 12 with 190 million unique users, 1.9 billion page views, and 10.2% reach. Twitter at No. 14 garnered 160 million unique users, 5.9 billion page views and 8.6% reach.