Identifying Unique Visitors

The method for identifying unique visitors among multiple contexts includes a prioritized sequence to ensure accuracy in this determination. The following table shows this prioritized sequence:

Order used Query parameter (collection method) post_visid_type column value Present when
1 vid s.visitorID 0 s.visitorID is set.
2 aid  s_vi cookie 3 Visitor had an existing s_vi cookie before you deployed the Visitor ID service, or you have a Visitor ID grace period configured.
3 mid AMCV_ cookie set by Identity Service 5 Visitor’s browser accepts cookies (first-party), and the Identity Service is deployed.
4 fid fallback cookie on H.25.3 or newer, or AppMeasurement for JavaScript 4 Visitor’s browser accepts cookies (first-party).
5 HTTP Mobile Subscriber header 2 Device is recognized as a mobile device.
6 IP Address, User Agent, Gateway IP Address 1 Visitor’s browser does not accept cookies.

For information on how unique visitors are reported, see Unique Visitors in Analytics.

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