Definition
Also written: lift testing, geo testing
Incrementality testing measures what a marketing activity actually caused, by comparing a group exposed to it against a comparable group that was not. Geographic holdouts, audience splits and time-based tests are the common designs, and the output is a causal estimate rather than an attributed share.
It answers the question attribution cannot: what would have happened anyway. Channels that capture existing demand — brand search especially — often show far less incremental effect than their attributed credit implies.
The cost is real. A holdout means deliberately not marketing to part of the addressable audience for the test duration, and small tests produce confidence intervals too wide to act on.
The usual error
Where this goes wrong in practice
Running a test too small or too short to detect the effect size that would change a decision, then treating an inconclusive result as evidence of no effect.
Related terms
Multi-touch attribution (MTA)
Multi-touch attribution distributes credit for a conversion across the marketing touchpoints that preceded it, using a rule (first touch, last touch, linear, time decay) or a data-driven model. It describes observed sequence; it does not establish that any touchpoint caused the outcome.
DefinitionMarketing mix modelling (MMM)
Marketing mix modelling uses aggregate historical data — spend, sales, seasonality, price, external factors — to estimate each channel’s contribution statistically. Because it works on aggregates rather than individual journeys, it is unaffected by cookie loss and consent restrictions.
DefinitionConsent mode
Consent mode is Google’s mechanism for adjusting tag behaviour according to a visitor’s consent choices, sending cookieless pings when consent is denied so that conversions can be modelled rather than simply lost. Its output is estimated, and reporting distinguishes observed from modelled data.
DefinitionGA4 key events
Key events are the GA4 events a property has marked as significant — the renamed successor to "conversions" in that interface. They drive reporting and can be imported into advertising platforms, and their counts may include modelled as well as observed data.
DefinitionOffline conversion import
Offline conversion import sends outcomes that happen outside the website — a qualified lead, a booked job, closed revenue — back to the advertising platform, matched to the original click. It lets bidding optimise toward revenue rather than form fills.
DefinitionPerformance Max (PMax)
Performance Max is a Google Ads campaign type that serves across Search, Display, YouTube, Discover, Gmail and Maps from one budget, with placement, audience and creative decisions automated. It reports far less channel-level detail than the campaign types it replaced.
Definition