Marketing Mix Modelling for senior marketers: When to trust the numbers (and when not to) 

A guide to getting MMM right

Trust in MMM isn’t a nice-to-have. It’s the difference between confident investment decisions and budget debates that go in circles. And right now, with privacy changes, fragmented journeys, and platform reporting getting noisier, senior teams are being asked to make bigger calls with less certainty. 

The good news: you don’t need “perfect measurement” to make better decisions than your competitors. You need the right framework, governance, and decision discipline. 

Below is a practical, senior-marketer-friendly guide: useful, actionable, and grounded in how MMM works in the real world. 

Unique and insightful expertise

It has never been more difficult to cut through measurement noise. While a model provides the data, it is the specialist’s ability to interpret those outputs, offering insights that are interesting, unique, and actionable, that elevates MMM from a static “report” to a strategic advantage. 

We’re seeing more demand for an authoritative measurement method, both in proactive planning and in reactive moments (e.g., “Why did performance dip last month?” or “Can we justify cutting TV?”). When MMM is positioned as a decision-support system (not a scoreboard), it gives leadership a calm, evidence-based way to respond. 

Whether you already have in-house analytics capability, or you’re working with an agency/partner, it’s worth considering how you build a consistent “expert voice” around MMM – one that can explain:

• What the model is confident about 

• What’s uncertain (and why) 
• What decisions it should and shouldn’t be used for 

MMM governance can be your superpower

Most MMM programmes don’t lose trust because the model is “wrong”. They lose trust because nobody can explain what changed, why it changed, and what to do next.  

Governance is the game changer and you need to stay on top of your measurement environment in the same way you stay on top of your market. Ensure you are: 

• Tracking changes 
• Naming / tagging changes 
• Channel definition changes 
• Promo / pricing / distribution shifts 
• Competitor shocks

Then, crucially: know how and when to react.

A practical governance approach looks like this: 

1) Create a change log (non-negotiable)

Every MMM refresh should have a simple log of what changed since last time:

• Data backfills 

• Attribution/tagging updates 

• Spend mapping changes 

• KPI definition changes 

• Structural market events (e.g., promo cadence, price changes)

If you can’t answer “what changed?” in one minute, you can’t expect senior stakeholders to trust the new outputs.

2) Use a “confidence ladder” to prevent over-reliance 

Not every result is decision-grade. Treat outputs like you would financial forecasting:

• Directional: good for learning and prioritising tests 
• Planning-grade: good for quarterly reallocations using ranges/scenarios 
• Finance-grade: suitable for big bets only when inputs and validation support it

This instantly reduces politics because you’re not forcing every channel into a single “truth number”. 

3) Set pre-agreed rules for when to downgrade trust 

This is where mature teams stand out. Agree in advance:

• What conditions make results less reliable (high correlation, tracking break, major KPI change) 
• What the business should do in those moments (act cautiously, test, or hold steady) 

That’s how MMM becomes safer – and more credible. 

Make it evergreen

MMM trust doesn’t come from one “perfect model run”. It comes from repeatability. Even if a specific output doesn’t land immediately internally, consistent MMM governance has a compounding effect over time. The teams that get the most value tend to:

• Keep channel definitions stable 
• Version their models and assumptions 
• Document methodology in plain English (not technical notes) 
• Build continuity so leaders see patterns, not surprises 

If you’re not seeing immediate “buy-in”, but you’re confident the foundations are strong — don’t panic. Trust is often earned through:

• Consistency across cycles 
• Clear explanation of uncertainty 
• Evidence that the team knows when not to overclaim

MMM becomes evergreen when it’s treated as an always-on capability, not a one-off deliverable. 

Be tactical when it comes to MMM outputs

There’s been a lot of debate about whether MMM can be “the source of truth” for everything. 

It can’t – and it shouldn’t try to be. MMM is at its best when it’s used tactically for the decisions it’s designed for, such as:

• Budget setting (quarterly/annual) 
• Scenario planning (“If we move £X from A to B, what happens?”) 
• Channel role clarity (what drives short-term vs longer-term demand) 
• Test prioritisation (where experiments will tighten uncertainty fastest) 

Where MMM is not the right tool:

• Week-to-week bid optimisation 
• Creative-level learnings 
• Diagnosing single-campaign performance in isolation

The most effective approach is layered:

• MMM for strategic allocation and guardrails 
• Experiments for incrementality confirmation where feasible 
• Platform and creative testing for execution speed 

When those layers work together, MMM stops being a debate and becomes a decision engine. 

Is there a monetary element?

Finance teams don’t just want insight – they want a number they can defend. And that’s where MMM often gets mishandled. If you want MMM to influence senior decision-making, give leaders money-grade framing:

• Ranges (expected / upside / downside) 
• Payback windows (weeks vs months) 
• Risk statements (“If we cut brand spend by X, here’s the likely impact range and the uncertainty”)

This allows you to talk about MMM like an investment committee would:

• Not “what’s the ROI?” 
• But “what’s the expected return and what’s the downside risk?” 

It’s also worth identifying where you can add monetary clarity through structure:

• Separating baseline demand vs incremental impact 
• Controlling for promotions, pricing, and distribution 
• Clearly stating what’s in-scope and out-of-scope

The goal is not to pretend MMM is perfectly precise. The goal is to make budget choices more robust than gut feel. 

Don’t forget the basics 

MMM can’t rescue weak fundamentals. And senior stakeholders will lose trust quickly if the basics aren’t right.

Always sanity-check:

• Channel mapping: are you comparing like-for-like spends? 
• KPI consistency: has “revenue” or “conversions” changed definition? 
• Non-marketing factors: are promo, pricing, distribution, and seasonality accounted for? 
• Correlation reality: are multiple channels moving together (making separation hard)? 
• Decision clarity: what will we actually change based on this output? 

One practical tip: try to include multiple perspectives so results don’t feel “owned” by one team.

• Bring finance in early 
• Align brand and performance teams on time horizons 
• Be clear about what the model can and can’t answer

If it feels like you’re forcing MMM to justify a pre-decided narrative, it probably won’t land. 

Summary 

Hopefully this has provided useful guidance for senior marketers on building MMM that people actually trust. The biggest takeaway: trust doesn’t come from the model alone. It comes from governance – decision clarity, stable definitions, transparent uncertainty, and a cadence that turns outputs into actions. No two MMM strategies should be identical. Your governance should reflect your business reality:

• Number of markets and channels 
• Data maturity 
• Test-and-learn capability 
• Leadership’s appetite for risk

Revisit your MMM approach regularly. Be honest about what’s stable, what’s uncertain, and what’s changed in the system. If scenario planning is consistently driving better decisions, double down on it. If month-to-month swings are creating doubt, invest in the change log, definitions, and validation. 

Ready to put these principles into practice? 

At Connective3, we’ve built these governance frameworks directly into Impact, our in-house Marketing Mix Modelling solution. Impact is designed to give senior marketers exactly what this guide advocates: clear confidence levels, transparent change tracking, and scenario planning that speaks the language of finance teams. If you’re looking to move beyond one-off reports to an always-on measurement capability you can trust, we’d love to show you how Impact can support your decision-making.