Standard attribution credits every touchpoint a customer encountered — but correlation is not causation. Incrementality testing measures what would have happened without your ads. We design and execute ghost ad tests, geo holdouts and matched market experiments that reveal your advertising's true incremental impact.
Incrementality testing measures the causal effect of advertising by comparing outcomes for groups exposed to ads versus matched holdout groups not exposed. Unlike attribution (which measures correlation), incrementality measures causation — the actual lift in revenue, purchases or customers that your advertising created.
Last-click attribution gives 100% credit to the final touchpoint before conversion — typically branded search or direct. This systematically under-credits prospecting channels (Meta, TikTok) that initiated the journey and over-credits retargeting, which often captures customers who would have converted organically.
Most incrementality tests require 2–4 weeks to achieve statistical significance — longer for campaigns with lower conversion volumes. Geo holdout tests for brand advertising may run 4–8 weeks. We calculate required test duration based on your baseline conversion rate and desired confidence level.
Incremental ROAS (iROAS) is the revenue generated per pound of advertising spend that would NOT have occurred without the advertising. It differs from reported ROAS by removing organic conversions that would have happened regardless of the ad. iROAS is the true measure of advertising's financial contribution.
Meta Conversion Lift tests require sufficient conversion volume to achieve statistical significance — typically £5,000–£20,000 in spend during the test period depending on conversion rate. Geo holdout tests require sufficient market-level revenue data to detect meaningful lifts.
Book a free incrementality testing session and design your first causal measurement experiment.