Measuring Site Performance (Part 3)

Popularity metrics are a set of yardsticks by which you can judge the relative popularity of your site over time. The primary metrics are:

  • Unique Visitors
  • Visits
  • Page Views (Impressions)
  • Average Visit Length

Your web server archives the information needed to generate these numbers and many others. The raw data is stored on the server in what is known as a log file. The statistics referenced above are best accumulated through the use of a log analysis program to convert your hard-to-read server log files into an understandable format. The most popular of these programs is WebTrends (www.webtrends.com).

Let’s take a quick look at each of these popularity metrics. The number of Unique Visitors is perhaps the most vital statistic as it counts the visitors to your site and then factors out double counting. (Note that this statistic is far more meaningful to you than the oft-referred to Hits statistic.  Hits simply tells you the number of files transferred from the server to the visitors’ computers. While this initially sounds good, it falls apart when you learn that a single web page can contain a large number of individual files, each of which is counted and contributes to the total Hits count. Hence the Hits number can be easily manipulated by site owners by varying the number of individual files on any page.)

Be aware that there are limiting factors in the counting. The primary impact comes from what are known as Masked IP Addresses, that is, networks that automatically give all their users the same IP Address.

An IP Address is an identifying number given to each computer connecting over the Internet. Servers use IP addresses as a convenient way to track visitors. This brings us to an important point: Unique Visitors does not count people, it counts computers, and that is the root of the problem.

The biggest Masked IP Address villain is AOL. All AOL users share the same IP address,  so when 35 people from AOL visit your site in a week, your number of Unique Visitors stat will count only 1 visitor.

Another limiting factor is multiple users on one computer. If all four members of my family visit your site one week, you only see one visitor in the number of Unique Visitors stat.

The Visits statistics gives the total number of visits to your website during the reporting period. It is a useful metric when used to temper the Unique Visitors stat for purposes of arriving at an accurate picture of the trend of activity on your site. Remember of course to factor out double counting as one person visiting the site 25 times in a week will show 25 visits. In other words, remember this is Total Visits, not Total Visitors.

Page Views (also called “Impressions”) tells you the total number of pages viewed by site visitors during the reporting period. So, if Visitor A looks at just the Home Page, but Visitor B explores the site, visiting 9 pages before leaving, Visitors A & B would be collectively responsible for 10 Page Views (1 + 9).

The Page Views number is also susceptible to a degree of miscounting, as cache files cause undercounting and search engine robots can cause over counting.  The cache files problem is very hard to detect and according to some sources causes up to 30% undercounting. The severity of the problem depends largely on both the way your site is built and how your server is configured. This is a complex problem to solve and if it is key to your efforts it should be discussed with your IT team or vendor prior to construction of the site.

Search engine robots (or “spiders”) can be easily factored out if you use a program such as WebTrends. WebTrends maintains a separate count of visits by robots, allowing you to adjust for them with an acceptable degree of accuracy.

The final primary popularity metric is Average Visit Length. Ever wondered if your site is sticky? This is the key indicator. This should be tracked across time for a trend. Content-heavy sites, subscription sites and sites relying on ad revenues obsess on this number as it indicates pretty clearly the success of their efforts to draw and hold an audience to their site.

The numbers above are primary metrics — key indicators. You can easily go beyond these numbers for more information, but the numbers above should the first stop for inquiries relating to how the traffic on your site is moving across time. Next column, we’ll look at a variety of eBusiness metrics.