Level: Advanced
Incrementality testing measures how many conversions genuinely wouldn't have happened without the ad, rather than simply counting conversions that occurred after someone saw it.
Standard Attribution Can Overstate Impact
Some conversions credited to an ad would have happened anyway, particularly for retargeting shown to people already planning to purchase.
Holdout Groups Reveal the Real Difference
Withholding ads from a randomly selected control group and comparing their conversion rate against the exposed group isolates the ad's genuine incremental effect.
This Is Especially Important for Retargeting and Brand Terms
These campaign types are particularly prone to overstated attribution, since they often reach people already close to converting regardless of the ad.
Next step: Use the Sales Letter Writer to if an incrementality test reveals a campaign's true impact is smaller than reported, review whether stronger, more genuinely persuasive creative could increase the real incremental lift, not just the attributed one.