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|
|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.|
|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.