Measuring Unique Web Visits

The number of unique visitors is a fundamental metric of Web analytics. These days, it's still used to measure the overall level of traffic to a site and is particularly important for those sites that are dependent on advertising revenues as a major source of income (Mason, 2010). Kaushik defines unique visitors as “The first time someone visits your site a first party persistent cookie is set in their browser. This cookie lasts any where from several months to several years. Each time that person visits your site that cookie identifies them as the same browser” or a simpler definition is “a count of all the unique cookie_id’s during a given time period.”

A unique visitor count is always associated with a time period (most often day, week,

or month), and it is a “non-additive” metric. This means that unique visitors can not

be added together over time, over page views, or over groups of content, because

one visitor can view multiple pages or make multiple visits in the time frame studied.

Their activity will be over-represented unless they are de-duplicated (WAA, n.d.).

The deletion of cookies, whether 1st party or 3rd party, will cause unique visitors to

be inflated over the actual number of people visiting the site (WAA, n.d.). Users that block cookies may or may not be counted as unique visitors, and this metric is handled in different ways depending on the analytics tool used.

One must know how your tracking software is defining visitors, so that you can then make accurate use of the data especially when comparing with other tools or reports.  Once you know how they are defined and can test the accuracy of the actual measurement, it is a good idea to study the data to find gaps, exceptions and errors that occur using these definitions and what impact they have on your numbers, and hopefully be able correct or account for these when reporting results.

Sounds simple enough, but the fact is that most software that tracks your visitors has different definitions of what defines and how to measure a unique visitor.  There are three major components to defining and measuring unique visits (ACS, 2009).

 

1.         How do you identify a visit as unique?

2.         Over what time period do you use to begin and end uniqueness?

3.         How do you measure it?

The measurement issue comes into play when a consumer visits the website a second time and either their device doesn't accept cookies, they have deleted the cookie, or they are using a new device or browser. The reality may be that they have visited that website before, but as far as the Web analytics system is concerned, the user doesn't have a cookie on their device and so it will treat them as a new visitor. As a result, the proportion of visitors who are considered to be new is generally an overestimate (Mason, 2010).

Image courtesy of Econsultancy

Google Analytics revealed a work-in-process solution last Spring (2013) that it would have the ability to track unique visitors using multiple devices with a single client ID working off the backbone of Google Universal Analytics (Brown, 2013).  While the mapping for Android and other devices has been outlined, we will need to stay tuned to see how they plan on handling Apple iOS to stitch the devices under a single ID.

On a lighter note, view this short video on WTMD (Way Too Many Devices) to see a parody on device overload and tracking unique visitors.