Two attributes characterize a cookie in terms of Web Analytics: its domain and its expiration date. It is often the cookie expiration date that determines the uniqueness of a visitor.
If the domain is the same as that of the site that is viewed, it is called first-party cookie. However, if the field is different from the site visited, we talk about third-party cookie. Most third-party cookies are generated by advertising to advertisers sites or Internet audience targeting.
Third-party cookies are often the target of tools or anti-spyware or anti-advertising filters that block the creation of cookies. Besides, the various mechanisms erase cookies, so the figures for unique visitors can be reduced from 5% to 40%. This large difference is an estimate because it is extremely difficult to accurately assess the blocking rate and/or deletion of cookies.
In general, the original cookies are less prone to blocking because are considered less intrusive than third-party cookies but they are still susceptible to erasure.
Campaigns: custom pages or inbound links?
Promotional campaigns related to web are the object of statistics analysis. This is called analytics SEO for analyzing positions on search engines of websites and SEA analytics for advertising campaigns.