Probabilistic Attribution

In one line

Probabilistic attribution connects a click to an install by matching patterns — device model, OS version, time window, IP range — instead of a unique identifier. It's used when a deterministic ID like IDFA isn't available.

Why it exists

Before Apple's App Tracking Transparency (ATT), a unique identifier could link a click and an install with certainty. Once users can decline tracking, that ID often isn't available, so probabilistic matching became a fallback way to estimate the connection.

Deterministic vs. probabilistic

• Deterministic matching: a unique ID links click and install with certainty. Accurate, but requires user consent.
• Probabilistic matching: contextual signals suggest a likely match without consent. Less privacy-invasive, but can be wrong.

Why to be careful

Mismatched attributions from probabilistic matching can inflate or deflate a channel's apparent performance. This is part of why channel-attribution methods that don't need individual tracking — like MMM — are getting renewed attention.

Go deeper

Other reasons attribution numbers diverge across sources are in Attribution Data Mismatch.