MMM Updates: Why they often happen based on Budget, and not when they are actually needed !!

One uncomfortable truth in Marketing Mix Modeling (MMM) is this:

MMM model updates are often driven by project budget, not by statistical or marketing necessity.

In many engagements, monthly or quarterly or even half yearly “updates” exist because the pricing model demands it, not because the model genuinely needs a rebuild.

But we all know that MMM models don’t decay on invoice cycles.
They decay based on data dynamics and marketing reality.

📌 Updates vs Total Rebuild

Adding one more month of data and re-running the same specification is not the same as rebuilding an MMM from scratch.

An update typically :

▪️Appends one new data point

▪️Re estimates coefficients under the same structure

▪️Assumes the underlying relationships are stable

📌 But Why MMMs decay over time

In the real world, marketing systems are non stationary. Over time, one would see:

– Media mix shifts

– Creative refreshes

– Pricing changes

– Distribution expansion

– Consumer behavior drift

All of this and more leads to model decay.

At some point, you are no longer “updating” a model . You are forcing old assumptions onto new data !!

📌 Our rule of thumb at Aryma Labs

At Aryma Labs, we deliberately separate:

Model updates from Model rebuilds

And the important part is:

We do NOT charge clients the full model build cost for every monthly update.

Instead, we follow a simple rule of thumb:

If around 6 months have passed since the last update, chances are you should rebuild the model from scratch.

📌 Why 6 months?

Because by then:

▪️Enough new data has accumulated to materially change estimates

▪️Structural shifts are likely to have occurred

▪️Re estimating without re thinking the specification becomes risky

Beyond a point, a update often becomes expensive misinformation.

When MMM updates are dictated purely by budgets, Clients pay for updates that add little incremental value. Vendors avoid rebuilding because it’s “out of scope”. Decision quality slowly degrades over time.

On the other hand, when MMM updates are dictated by data sufficiency, market shifts and model health:

✅ Rebuilds happen when they are statistically justified

✅ Incrementality and attribution estimates remain credible

📌 Bottom line

Updating too often without rethinking marketing reality structure is misleading.

Waiting too long to rebuild could also be dangerous.

Good MMM practice isn’t about how often you can update a model.
It’s about knowing when the old one has stopped telling the truth.