## How Wrong Is Your Marketing Mix Model (MMM)? A well-built MMM can still be wrong, because the spend it learns from never held the information it needs. This article tests whether changing when you spend, not how much, can fix that. Measuring the return on marketing spend is one of the hardest jobs in growth, but Marketing Mix Modelling has had a resurgence as the answer to it in recent years. Open-source releases have driven most of that: Robyn from Meta, Meridian from Google, PyMC-Marketing from PyMC Labs. Running an MMM has never been easier. Trusting one is a different question. Google…