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Understanding Hits, Page Views and User Sessions
When analyzing web site traffic, there are a number of measures that are used to report on activity and volume of visitors. Because of this, there is often confusion as to what the various measures actually mean, and how they are calculated. This document explains the key methods for measuring traffic to a web site, what the differences are, and the associated statistics that appear in WebTrends reports.

When reading this document, it is important to have a high level understanding of how Web sites deliver information to a browser. When a user clicks on a link, or types in a URL in the address line in their browser, they are actually sending a request to a server to send specific information, contained on a page. Part of this request is the IP address (or return address) of the user’s computer, so the server knows where to send the page. The page may contain various elements, or files, such as HTML text, graphic images, such as .gif, .jpg, .bmp, audio or video files, etc. As the server responds to this request, it writes a summary of the action into a log file. WebTrends products read these log files, and analyze, summarize and report on the contents in an easy to understand manner.

Methods for Measuring Web Site Activity
The three most common measurements of web site activity are hits, page views and user sessions. Following is a description of each.

Total Hits is the total number of files that are requested from the server. This includes all graphics, audio/video files, and other supporting files, as well as the actual html page itself. Total Hits includes all requests in the count whether or not the files were successfully retrieved. Total Successful Hits, on the other hand, are only those files that were successfully served.

Page Views, or Page Impressions is the number of pages viewed. Pages are files with extensions such as .htm, .html, .asp (and a few others). (With WebTrends, you can see (and edit) the full list by clicking Options |Web Log Analysis | File Types, and then Document File Extensions.) Impressions, therefore, are a count of the number of pages viewed and do not include the supporting graphic files. Thus, by definition, you should have more total hits than page views. For instance, if a site has 1 web page with 5 graphics on it, every time a user visited that page, it would be reported that 6 hits and 1 page view or impression occurred.

User Sessions is the number of unique users who visited a web site during a certain time period. Measuring user sessions is more complicated than measuring hits or page views. The user session statistic can be seen as equivalent to "Unique Visits," which, unless every visitor only sees one page, will be less than the number of page views/impressions.

Methods for Counting User Sessions
The most accurate way to count user sessions is for the site to require that every visitor use a unique username/password combination before entering the site. This would ensure that the log file contained information that uniquely identified every user. WebTrends uses this information in the "authenticated user" tables.

Obviously, requiring every visitor to have an username and password is not going to viable in every situation. Therefore, many web sites use cookies to uniquely identify their visitors. Cookies are pieces of software code that reside on the hard drive of the client (or requesting) computer that contain information that identifies the computer to the server. There are problems with using cookies, however, when trying to track unique user sessions. First, some people may refuse to accept cookies. Second, cookies can be erased from the client hard drive. This could result in double counting unique visitors during a period if the visitor deleted her cookie between visits. Finally, there is no way to know if the client computer is a shared computer between many unique visitors.

The final way to track user sessions is through the IP address of the visitor. Every record in the log file contains an IP address, as this is how the server knows where to send the information that has been requested. The limitation to counting unique IP addresses, however, is that many Internet Service Providers and companies use various methods that skew the analysis. Some organizations use dynamic ISP addressing where an IP address can be determined dynamically when a user logs in, through the use of firewalls, or by a load-balancing device. Others, such as AOL, filter all data so it comes through an intermediate proxy server. In this case, the Web server sends the requests not to the individual requestor, but to the proxy server of the ISP. The information is then sent on to the actual visitor, but with the source address of the proxy server.

Calculating user session information, therefore, involves a number of assumptions. User identification is based on authentication, cookies, or IP address. Those users that either have a unique cookie to identify themselves or authenticate on your server reflect an accurate count of visitors, as they are independent of IP address or proxy server use. But as noted before, it isn’t necessarily viable in all situations to make users authenticate through username/password, and not every user will accept an identifying cookie in their browser, so the third option of basing user counts on IP addresses is used.

To count a user from an IP address a number of assumptions must be made. The first assumption is to count a user for a particular IP as new/unique if the server has no record of activity for a certain amount of time(30 minutes is the default in WebTrends products, but this can be modified). Remember that the Internet functions as a series of requests. The server sees each of these requests as separate and distinct. Analysis software, such as WebTrends products, analyzes and reports on these distinct requests in a meaningful manner. So the first assumption used is that if we detect a series of requests being sent to a particular IP address within a defined time frame, we count these requests as a single user session. If there are no requests within a particular time frame, the next time a request comes in to send information to that particular IP address, we count that request as a new user session.

The limitations with this scheme are twofold. The first limitation lies with the use of dynamic IP’s or proxy servers at ISPs, as discussed above. If User A visits a site and immediately leaves, but User B comes to the site within the time frame defined, using the same source IP address, both visitors will be counted as 1 visitor. If, on the other hand, User A visits the site then goes and gets a cup of coffee, or attends a meeting which exceeds the defined time frame (ie 40 minutes), only to return to the site and pull up a second page, she would be counted as 2 users.

All log file analysis software that counts users has to work under some set of assumptions similar to those described above. User Sessions do, however, give a good idea of how many people are visiting the site and are the only successful way to track individual visits using current technology.

Article courtesy: Web Trends

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