Both models are wrong. One is wrong usefully.
Attribution does not measure causation and was never able to. The question is not which model is accurate — it is which set of errors you can work with.
Our bias, declared
We use data-driven attribution for allocating budget within a channel and geo holdout tests for deciding whether a channel deserves budget at all. Anyone claiming an attribution model tells you what caused a sale is selling you something. Every model distributes credit among touchpoints that were observed; none of them can tell you what would have happened if the touchpoint had not existed, which is the only question that matters when you are deciding whether to spend more.
Side by side
| Factor | Data-driven | Last-click |
|---|---|---|
| Credits upper-funnel touchpoints | Yes, proportionally | Never |
| Transparency of the maths | Proprietary, not inspectable | Completely obvious |
| Stability month to month | Shifts as the model retrains | Rock stable |
| Minimum data required | Meaningful conversion volume | Works at any volume |
| Reproducible by your analyst | No | Yes, in a spreadsheet |
| Reflects assisted conversions | Yes | Discards them entirely |
| Bias toward branded search | Reduced but present | Severe — brand takes the credit |
| Usefulness for in-channel bidding | Strong | Systematically misallocates |
| Answers 'is this incremental?' | No | No |
| Cross-device coverage | Modelled where signal allows | Breaks at the device boundary |
Choose data-driven when
You are allocating budget inside one platform
This is what data-driven attribution is genuinely good at. Given a fixed channel budget, it distributes credit across campaigns and keywords far more sensibly than last-click, which hands everything to the final branded search and starves the campaigns that created the demand.
Your funnel has multiple real touchpoints
Considered purchases with a six-week window and five interactions are exactly where last-click misleads most. Any model that acknowledges the first four touchpoints existed will allocate better than one that pretends they did not.
You have the conversion volume to support it
Data-driven models need enough conversions to fit anything meaningful. With healthy volume the model is doing real work; below that threshold it is producing confident-looking numbers from noise.
Choose last-click when
You are debugging, not allocating
When you need to know exactly what happened — which click, which landing page, which sequence — last-click's simplicity is the feature. Nobody can argue with the number because anyone can reproduce it, which matters more than accuracy during a diagnostic.
Volume is low and the model would be fitting noise
Below meaningful conversion volume, a data-driven model produces unstable weights that shift every retrain. Last-click will be biased, but it will be biased consistently, and a consistent bias is something you can mentally correct for.
You need a number that does not move
For year-on-year comparisons and any figure a CFO will hold you to, a model that silently retrains is a liability. Last-click's stability is why finance teams keep asking for it even when marketing objects.
What the disagreement is actually costing you
The two models will not agree, and the gap is not small — in most accounts we audit, upper-funnel campaigns look two to four times better under data-driven attribution than under last-click. Neither figure is the truth. Both are distributions of credit across touchpoints that were logged, and both attribute one hundred percent of every conversion to marketing, including the customers who were going to buy regardless.
That last point is the expensive one. Branded search is the clearest case: someone who already decided to buy searches your name, clicks an ad, converts, and both models record a conversion. Turn the campaign off and most of that revenue arrives through the organic result immediately below. We have seen brand campaigns with reported ROAS above 20x whose true incrementality was close to zero.
The resolution is not a better model. It is a holdout: switch a channel off in a set of matched regions, run it long enough to clear the purchase cycle, and compare total revenue against control regions. It costs you real revenue in the test markets and it is the only method here that answers the causal question. Run it once a year on your largest channel and use attribution for everything below that decision.
Related questions
One, consistently, with the method written down — and total revenue alongside it. The failure mode we see most often is a deck that quietly switched models between quarters, making a flat channel look like growth. Whichever you pick matters far less than not changing it silently, because the moment attribution methodology becomes a variable, no trend in the deck means anything.
Other comparisons
Services referenced
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