Marketing mix modelling (MMM)
MMM is a statistical approach that estimates each channel's contribution to outcomes using aggregated historical data - spend, sales, seasonality, pricing, external factors - without tracking individuals. It answers allocation questions at a strategic level and has regained prominence as user-level tracking declines.
In practice
MMM's strengths are privacy-independence and cross-channel comparability, including offline; its limits are data requirements, granularity and the lag between question and answer.
For most small and mid-size advertisers, the practical ladder is clean tracking and pacing first, incrementality testing second, modelling when scale justifies it.