THE SHORT ANSWER
Marketing incrementality is the difference between the outcome observed with an intervention and the outcome that would have occurred without it. Because the same person cannot be observed in both states at once, experiments or carefully justified comparison designs estimate that counterfactual.
The missing outcome is the central problem
A person who bought after seeing an ad may also have bought without it. A person who did not buy might have been influenced later. Platform conversions record attributed outcomes under platform rules; incremental conversions estimate the additional outcomes caused by the activity.
Base or organic demand includes outcomes expected without the tested intervention. It is not always literally organic-channel traffic.
Choose a comparison the decision can support
| Design | Comparison | Challenge |
|---|---|---|
| User holdout | Eligible people withheld from treatment | Identity, contamination and platform access |
| Geo experiment | Comparable regions with different treatment | Spillover and regional comparability |
| Time-based interruption | Outcome before and after a change | Seasonality and simultaneous changes |
| Matched observational comparison | Similar treated and untreated units | Unmeasured differences remain |
Define lift and cannibalisation carefully
Absolute lift is the difference in outcome between treatment and the estimated control. Relative lift divides that difference by the control outcome. The same absolute change can produce different relative percentages depending on the base.
Cannibalisation occurs when measured activity shifts an outcome from another channel, product, time or customer group rather than adding value overall. Inspect total business outcomes and mix, not only the treated surface.
Reserve causal precision for valuable decisions
Experiments have cost and operational constraints. Use them where uncertainty could materially change budget, channel, product or customer treatment. State when randomization was unavailable and which assumptions support an observational estimate.
Read Marketing Attribution for credit assignment and the Performance Marketing overview of attribution limits for campaign application.
Evidence & context: Google Research
Sources & further reading
- Methods for Measuring Brand Lift of Online Ads
Google Research. Original research using randomised experiments to estimate advertising effects; no universal lift or ROI benchmark is inferred.
- Get started with attribution
Google Analytics Help. Official definitions of current GA4 attribution settings and models. Product options can change, and assigned credit is not the same as incremental impact.
- About modeled key events
Google Analytics Help. Official description of modeled key events under observation gaps. Modeled values remain estimates and may differ across reporting surfaces and processing times.
Examples and exercises are illustrative unless attributed to a source. No independent expert review is claimed.
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