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.
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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. There will almost always be more hits than page views
or user sessions.
Hit
is the request by a client for a document on our account. If a
person visits our homepage and there are 9 images on that page that counts
as 10 hits. 1 hit for the html document and one hit for each of the 9
images on that document.
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). 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.
There will almost always be more page views than user sessions
but less page views than total hits.
Document Views
generally include all static content, such as complete html pages.
We have gone to tracking
Document Views because of how our banner management system
delivers ads. Web Trends tracks pages and our banners as the same
but it tracks
Document Views in a more conservative and accurate way.
There will almost always be more page views than document views.
Effective Sept. 2004
There will almost always be more hits than
page views or user sessions.
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. Synonym: Visit or Visitor.
There will almost always be less user sessions than hits or page views.
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 a username and password is
not going to be 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.
There will almost always be more page views than
user sessions but less page views than total hits.
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.
There will almost always be less user sessions
than hits or page views.
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.
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