Probabilistic attribution on iOS: legal, useful, and constantly misunderstood

Probabilistic attribution on iOS: legal, useful, and constantly misunderstood

With ATT killing IDFA at scale, fingerprinting-based probabilistic matching is back — but it's not the deterministic crutch some buyers treat it as.

✓ Fills the gap SKAN leaves for click-through and immediate post-install behavior
✓ Works on signals like IP plus user-agent plus timestamp within a short window
✗ Apple's stance: probabilistic methods that fingerprint violate policy — vendors walk a gray line
✗ Accuracy decays fast beyond a 24-hour click window; long windows produce garbage matches

Use it as directional, never as ground truth. Reconcile probabilistic install counts against SKAN aggregate totals — if probabilistic claims more installs than SKAN reports total, your matching is over-crediting.

Verdict: useful as a same-day directional signal, dangerous as a system of record.
Best for: UA teams supplementing SKAN with short-window matching.