A Match ID is a cross-device identifier that sticks with a person over time.
Once Screen6 has identified a cluster of User IDs that belong to the same person, such cluster will get assigned a Match ID. Over time, the User IDs within the cluster may change; new ones come in, others disappear. However, the Match ID for this cluster will remain the same.
The User IDs that get linked to a Match ID can come from a mix of any type: cookies, IDFA's, MAC addresses, Smart TV IDs, etc...
Persistency: Match ID vs User ID decay
User IDs, cookies in particular, tend to disappear over time; sometimes slowly and sometimes immediately. These User IDs will get linked to Match IDs no matter their own level of persistency. This makes Match IDs much more persistent than User IDs.
Decay of Match IDs vs User IDs over days
Persons and Households
Devices that are shared amongst family members and that are not predominantly used by one of the members will not be attributed to a Match ID, however they will be attributed to a Household ID. Match IDs relate to persons, not households.
In an ideal case a person has only one Match ID that links all of the devices and IDs of this person.
However there are cases where our algorithms have linked for example the IDFA to the cookies of someones phone, and tablet IDFA to a desktop cookie of the same person in separate clusters. In such a case a person will have two Match IDs. These may still get linked at a later point in time.
Effects of probabilistic matching
It doesn't happen a lot, but in some cases our algorithms, which are probabilistic by nature, may decide that two Match IDs belong to the same person or that a User ID connected to a Match ID actually belongs to another Match ID. This results in movements in the graph.
When it's decided that two Match IDs belong to one person, the Match ID that has the fewest User IDs linked will be disposed and its User IDs are moved to the other Match ID.
When it's decided that a User ID actually belongs to another Match ID it is simply moved over to that Match ID.