Modern Bayesian Marketing Mix Modeling (MMM, powering Meta's LightweightMMM, Google Meridian, and Robyn) establishes aggregated top-down marketing attribution and budget optimization in privacy-first, cookie-less environments; Classical OLS fails by ignoring non-linear media physics; Modern Bayesian MMM introduces 2 foundational non-linear transformations: 1) Adstock Carryover Decay (Geometric or Weibull decay): modeling sustained brand memory persistence where past advertising impacts future weeks:
xt∗=xt+θxt−1∗; 2) Diminishing Returns Saturation (Hill Saturation Function): capturing saturation plateaus where marginal returns diminish at high spend:
Saturation(x)=KS+xSxS; Calibrated using Markov Chain Monte Carlo (MCMC via NUTS in PyMC/Stan) incorporating informative Bayesian priors from randomized Geo-Lift experiments.