Identifying users across devices is even more difficult, especially with GDPR and CCPA. There are two methods — deterministic matching and probabilistic matching.
Deterministic methods match user profiles across devices. This method requires a unique identifier per profile. For example, if a user is logged into a service on two different devices, the service provider can use a unique identifier for the user. If the user views or clicks on an ad on one device and converts on another, the deterministic method will be able to match the user through this unique identifier. This results in a higher confidence rating that a profile has been matched on a laptop to a mobile device, although it may under-report the true number of conversions.
Probabilistic methods match multiple and more generalized signals across devices. Those signals are more vague. For example, a geolocation tied to a phone owned by a male interested in baseball versus the same geolocation tied to a laptop owned by another male living in the same neighborhood interested in baseball. This method will generate a high probability of a match but it may result in situations where two users end up with the same ID.
FuelX is integrated with Google Display & Video 360 and Google Campaign Manager. We rely on the deterministic matching from Google and a user’s Google ID (or “GID”).
Read More about Deterministic and Probabilistic Matching from ClearCode