Speaking of measuring your web site traffic, one of the most common and important metric is the "unique visitor". We want to know how many individuals visited our web site versus how many clicks or hits occurred. A unique visitor is an individual who comes to your site and is only counted once during a given period regardless of how pages they visit, clicks made or actions taken while on your web site.
Sounds simple enough, but the fact is that most software that tracks your visitors have different definitions of what defines and how to measure a unique visitor. There are three major compontents to defining and measuring unique visits. The first is how do you identify a visit as unique, the second is over what time period do you use to begin and end uniqueness, and the third is how do you measure it. The accuracy and usefullness of your unique vistior measurements will be relative to these factors.
A common defintion of a Unique Visitor is the use of IP address and browser id, other methods include defining cookies and session ids.. Time of uniqueness is often defined as a 24 hour period with a limit 29 minutes of inactivity before it is considered a new visit. So that for example, a unique visitor could have many visits during a given day, but once a new 24 hr period begins that unique visitor is counted as a new visitor. This also plays a critical role in the definition of repeat visitor which is often used as segment of visitor for measuring traffic and ultimately the quality of your web site. The main point to remember is that one must know how visitors are being defined by your tracking software 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 defintions and what impact they have on your numbers, and hopefully be able correct or account for these when reporting results.
