Unique Visitors


The number of inferred individual people (filtered for spiders and robots), within a designated reporting timeframe, with activity consisting of one or more visits to a site. Each individual is counted only once in the unique visitor measure for the reporting period.


Authentication, either active or passive, is the most accurate way to track unique visitors. However, because most sites do not require a user login, the most predominant method of identifying unique visitors is via a persistent cookie that stores and returns a unique id value. Because different methods are used to track unique visitors, you should ask your tool provider how they calculate this metric.

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.

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. 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. Ask your tool provider how blocked cookies are managed in their tool: it is important to understand how this impacts other metrics with regard to these visitors.

By AFS Website Analytics.

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