Picking An MMM

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The story: measurement is quietly becoming a battleground. The two biggest ad sellers, Google and Meta, control or influence the "free" tools that grade every channel's performance.

Google's open-source MMM (marketing mix modeling, a statistical method that estimates how much each ad channel drove sales, using aggregated data instead of tracking individual users) ships with default settings that flatter Google, and reps are reportedly paid on adoption.

What's actually being decided: whether agencies, publishers, and measurement vendors let the sellers own the scorekeeping, or invest to keep it neutral.

Reversibility: Type 1 for the market (once Meridian becomes the default substrate inside agencies, it's sticky and hard to dislodge). Type 2 for any single operator (you can audit or swap your config tomorrow).

Forcing function: none acute. This is a slow-moving structural shift, not a dated event. Impact is genuinely low for programmatic plumbing (DSPs, SSPs, trading desks) and high for measurement leads, agency planners, and non-Google/Meta media sellers.

The Market Analyst: Follow the incentive, not the press release. Google giving away Meridian isn't philanthropy; it's distribution. If Meridian becomes the base layer inside agencies and measurement vendors, Google shapes how every dollar of cross-channel spend gets valued without touching a single bid. That's a cheaper, more durable moat than winning any auction. The tell is the commissioned sales force behind a "free" product. Meta's retreat from Robyn is the revealing move: they've conceded they can't win the modeling layer, so they're gaming it instead. Plain version: the referees are now sponsored by two of the teams, and one team just fired its own referee to go lobby the other's.

The Skeptic: This whole argument only holds if default settings meaningfully swing outcomes at scale. Maybe, but MMM has always been analyst-dependent and priors-driven. That's not new corruption; it's how the method works. Henry N.'s "free puppy, not free beer" line cuts both ways: a tool nobody customizes produces garbage regardless of whose thumb is on the scale, and sophisticated agencies do customize. Also note both AdExchanger speakers have editorial reasons to frame platform behavior as sinister. The hot-zone change is documented as a UX tweak, and "deliberate manipulation" is interpretation, not admission. The scandal here is thinner than the framing suggests.

The Operator: Tuesday morning, this is a config-audit problem, not a strategy crisis. If your agency runs Meridian white-labeled, someone needs to actually inspect the priors before results hit a client deck. Most teams don't have a data scientist to do it. That's where it breaks first: you're presenting a Google-flattering read and calling it neutral. Second-order effect at 90 days: a client's own Google rep and your MMM output agree suspiciously often, and eventually a non-Google seller (a CTV publisher, a retail media network) challenges why they're undervalued. Have the audit trail ready before that meeting, not after.

The Customer / End User (the non-Google/Meta media seller): This is where the real loss lands. If you're a publisher, an independent CTV platform, or a retail media network, and your channels get systematically discounted by default model priors you never see, you lose budget you earned. Invisibly. Nobody sends you a rejection email; you just don't get renewed. The defensive play: demand to know what MMM your agency clients use, and push for your channel to be represented with proper priors. Plain version: if the test that decides whether your ads "worked" is written by your biggest competitor, you're going to fail it a lot.

Where they part ways:

1. Is this corruption or just how MMM works? The Market Analyst sees a structural land-grab; the Skeptic sees a decades-old analyst-dependent method being sensationalized. Both can't be fully right. The truth hinges on how many adopters actually leave defaults untouched.

2. Who bears the cost? The Operator frames it as a manageable audit task; the non-Google seller frames it as existential and invisible. The gap is who has the leverage to demand the audit. Big agencies do. Small publishers don't.

What it hinges on: one measurable fact. What share of Meridian deployments run on or near default settings? If most customize (Skeptic's world), the "Google-friendly priors" problem is contained to the unsophisticated tail. If most don't (the reporting's implication, backed by the "free puppy" economics), then the default is the market, and Google has quietly bought the scorekeeping function.

The council leans toward the reporting being directionally right but overcooked: Meridian adoption is real and self-serving, but "manipulation" is stronger than the evidence. The move for operators isn't panic. Treat MMM outputs as adversarial by default and audit the priors, especially where a seller supplied the tool.

What to verify before acting: ask your measurement vendor or agency, in writing, (1) which MMM they run, (2) whether it's customized off defaults, and (3) how non-Google/non-Meta channels are represented in the priors. If they can't answer cleanly, that's your answer.

Prediction: Neither Google nor Meta will publicly disclose the default channel priors inside Meridian (or their MMM data feeds) by the end of Q1 2027 earnings season, and no major industry body (IAB, MRC, ANA) will have issued an MMM neutrality/auditing standard by then.

Confidence: Medium. Silence serves both sellers; standards bodies move slowly.

Why: The entire commercial value of a "free" MMM as a distribution moat depends on the priors staying opaque. Disclosing them would surrender exactly the advantage the reporting describes, so Google has a direct incentive not to publish them. Meta's shift from owning Robyn to influencing third-party reports shows even the second-largest seller has given up on transparency as a strategy. Industry standards bodies have talked about measurement neutrality for years without shipping enforceable audit frameworks (see the multi-year MRC/currency debates in CTV), so expecting a binding MMM standard within ~two quarters cuts against the track record. Voluntary disclosure or a fast new standard would require the incumbents to act against their own economics. That's the less likely path.

Revisit by 2027-04-30: We're right if neither platform has published default-prior documentation and no major body has issued an MMM auditing/neutrality standard. We're wrong if Google or Meta publicly discloses Meridian/feed default priors, or if the IAB/MRC/ANA ships an MMM neutrality standard, before that date.