Garbage in, garbage out. If a media mix model has any chance of working, the model has to be fitted on high-quality, accurate data.  Keep in mind: marketing mix models are holistic models operating at an aggregate level, not at an individual channel level. What that means is that if any of the data isn't correct, it puts the whole model in jeopardy. Bad data from one small marketing channel can cause a ripple effect that can negatively impact all of the other estimates in the model, so it's critically important to have a process and tools for validating the data quality that's being used by the model and as part of your business's incrementality system. In the context of…