When Apple released iOS 14.5 in April 2021, it introduced App Tracking Transparency (ATT) — a prompt that asks users if they want to allow apps to track them across other apps and websites.
Approximately 75% of users said no.
For advertisers, this was a crisis. Facebook's entire attribution model depended on tracking users from impression to conversion. Without that data, Facebook couldn't tell you which ad drove which sale.
Five years later, the dust has settled. We know what works in a privacy-first world: Marketing Mix Modeling.