Full Answer

Meta needs to connect a conversion event (a purchase on your website) to a specific Facebook user account to count it as an attributed conversion. EMQ measures how often that match succeeds. A score of 4 means Meta matches roughly 40% of events to a user profile; a score of 8 means 80%+ are matched. Unmatched events are invisible to ad attribution and audience building.

Why it compounds: Poor EMQ means Meta builds lookalike audiences from an incomplete buyer pool. The lookalikes drift toward the 20–40% of buyers whose purchases Meta could attribute — not your full customer base. Ad delivery gradually shifts toward lower-intent audiences, ROAS drops, and the root cause appears to be creative fatigue or audience saturation when it's actually an identity matching problem.

Top EMQ boosters: (1) Hashed email address — single highest-impact identifier. (2) Phone number — second highest. (3) fbclid — the click ID from the Facebook ad, links directly to the campaign click. (4) External ID — your internal customer ID, used for deterministic matching across sessions. Together these routinely push EMQ from 4–5 to 7–9 on purchase events.