If you check in on FR five times in a day, that is five visits. But you are just one "unique visitor" who visited FR five times. Another term is "page view" which is how many times you viewed a new page, which is larger than the number of visits. People looking to inflate their statistics will quote "page views" or "visits." But the true indicator of how many people are visiting a site are is the number of "unique visitors".; Which actually could be higher than the stats show because if both you and your wife visited FR twice (once each) using the same computer, the stats would show just on unique visitor since it is based on logging your computer's IP address.
http://www.comscore.com/method/method.asp
comScore Methodology
With more than 2 million participants under continuous measurement, the comScore Global Network is the largest consumer panel of its kind, and delivers the most comprehensive view available of consumer activity – both online and offline.
comScore has developed a statistical methodology to ensure the accuracy and reliability of projections to the total population based on its network. Ultimately this provides comScore clients with confidence in the quality of information that drives important business decisions every day.
At the heart of the comScore Global Network is a sample of consumers enlisted via Random Digit Dial (RDD) recruitment - the methodology long endorsed by many market and media researchers. comScore also employs a variety of online recruitment programs, which have been time-tested through the years in which the comScore Global Network has been in operation. The reliance upon comScore services by hundreds of clients stands as testament to the strength and reliability of this combined approach.
Participants in the comScore Global Network receive a package of benefits that have proven to be broadly appealing to all demographic segments:
Server-based virus protection
Attractive sweepstakes prizes
Opportunity to impact and improve the Internet
Participants are protected by industry-leading privacy policies that ensure anonymity of personal information.
Membership is provided through an efficient sign-up process.
All demographic segments of the online population are represented in the comScore Global Network, with large samples of participants in each segment. For example, our network includes hundreds of thousands of high-income Internet users - one of the most desirable and influential groups to measure, yet also one of the most difficult to recruit.
comScore determines the size and characteristics of the total online population via a continuous survey spanning tens of thousands of persons over the course of a year. The sample of participants in this enumeration survey is selected via RDD methodology. Respondents are asked a variety of questions about their Internet use, as well as descriptive information about themselves and their households. The result is an accurate and up-to-date picture of the universe to which the comScore sample is projected.
The resulting combination of large samples across all segments, and a reliable view of the total universe, allows comScore to eliminate the effects of over- or under-representation of any group in the network.
comScore services are based either on the complete Global Network database or from components relevant to client needs. For example, comScore's industry-leading, RDD-based Media Metrix 2.0 audience measurement system is founded upon 120,000 U.S. panelists. Media Metrix Global Services are produced using the behavior of 500,000 panelists outside of the U.S. And Media Metrix XPC (eXPanded Coverage) adds visibility of smaller Web sites and local market activity through data captured from the balance of the comScore panel.
comScore's Statistical Services team is comprised of industry experts with decades of experience in the unique science of continuously projecting sample-based data for consumer research.
For more information about comScore Networks methodology, please contact info@comscore.com.
It is actually more complex than just the IP address. Several fields are combined to try and narrow it down even further.