Data & identity
Deterministic matching
Deterministic matching links identifiers to the same person using definite, shared information, such as the same login email or phone number, rather than statistical inference.
Deterministic matching is certainty by evidence. If you sign in to a streaming service with the same email on your phone, laptop and TV, the service knows for sure that those devices belong to one account. That link is deterministic.
In advertising, deterministic signals include logins, hashed emails, phone numbers, customer IDs and loyalty numbers. Unified ID 2.0, RampID and walled-garden identities are built largely on deterministic data. It is the most accurate way to build an identity graph, and it powers match-based targeting such as customer-list uploads.
The trade-off is scale: only people who log in or share an identifier can be matched, often a minority of a publisher's audience. Deterministic does not always mean the same human, either: shared accounts and family devices blur the line. And "deterministic" claims should be checked, because some vendors extend deterministic links to unauthenticated devices, which is the controversy behind ID bridging. Compare probabilistic matching.
Think of it like this
Deterministic matching is like recognising two letters as from the same person because both carry their signature, rather than because the handwriting looks similar.
An example
A retailer uploads 1 million hashed customer emails to a social platform; 620,000 match signed-in accounts deterministically, a 62% match rate.
Related terms
Probabilistic matching
Probabilistic matching links devices or identifiers to the same person or household using statistical inference from signals like shared IP address, location, timing and device traits, with some uncertainty.
Identity graph
An identity graph is a database that links the many identifiers belonging to the same person or household, such as emails, device IDs, cookies and IP addresses, into one profile.
Hashed email
A hashed email is an email address transformed by a one-way cryptographic function, usually SHA-256, into a fixed string used to match users across systems without sharing the plain address.
ID bridging
ID bridging is attaching an identifier observed in one context, such as a hashed email from a logged-in session, to impressions in other browsers or devices where it was not directly observed.
Unified ID 2.0 (UID2)
Unified ID 2.0 (UID2) is an open-source advertising identifier, originally developed by The Trade Desk, generated from a user's hashed and salted email address or phone number with their consent.
Sources: Unified ID 2.0