Unique Visitors are the individually-counted users of a website. This KPI in online marketing and media planning shows how many people have visited a website during a certain period of time. Unique visitors shouldn't be confused with Visits and Page Impressions.
Cookies are utilized to determine the number of unique visitors to a website. When users visit a website from their Browser, a cookie is stored on their computer. This contains data, which can be used to uniquely identify the respective browser. If a user visits a website repeatedly, this is automatically registered by the cookie. Although he visits the site several times, he is only considered as one unique visitor. At the same time, he will of course create several visits and even more Page Impressions.
The terms “Unique Visitors,” “Visits” and “Page Impressions” are frequently confused. They are directly related to each other, however, they each refer to completely different parameters:
The following example will illustrate this. Let’s assume a website gets the following visits in one day:
Visitors 1 visits the website at 10:00 a.m., 1:00 p.m. and 5:00 p.m. and views two subpages. Visitor 2 visits the website at around 7 p.m. and views 13 subpages. Visitor 3 visits the website at around 8.00 a.m. and 11.00 a.m. and views three subpages one time and seven the other.
The evaluation result would be this:
When determining the unique visitors by means of cookies, there are inaccuracies, which ultimately result in inaccurate measurements. Such inaccuracies may be occasioned by the following circumstances:
This problem can only be circumvented by having user accounts with each user uniquely identifying themselves. However, since this is not always feasible in practice, a certain measurement inaccuracy is acceptable.
Unique visitors are an important indicator of the success of a website with regard to search engine optimization. Using this statistic, the traffic to a website can be better segmented. New and returning visitors can be differentiated from one another. How to evaluate unique visitors with Google Analytics is shown in this YouTube Video.