Two different metrics answer two different questions about your marketing spend. Using only one leaves money on the table.
Most marketing teams measure their spending the same way: they watch customers touch a channel (click an ad, view an email, land on a landing page) and then assign that channel credit if a conversion happens later. That's attribution. It dominates marketing analytics because it's simple and feels objective. But it answers only one question: which observed touchpoints should get credit for a conversion?
Attribution has a fatal blind spot. A customer who was already planning to buy might see your ad, click it, and convert. Your attribution model happily assigns that channel credit. But here's the reality: they were going to convert anyway. Your ad didn't cause the sale. It just happened to be the last touchpoint before a decision that was already made.
That distinction matters enormously for budget allocation. If you're spending based on attribution alone, you're probably overpaying for channels that mostly capture existing demand rather than channels that create new demand.
Incrementality asks a fundamentally different question: would this conversion have happened without my marketing? According to Search Engine Land, incrementality and attribution use different forms of evidence because they're solving for different problems.
Incrementality testing works by comparing what happens when you run a marketing activity versus when you deliberately pause it. If your conversions drop when you stop a paid search campaign in a test region, that drop is truly incremental revenue you drove. If they don't drop much, that channel was mostly capturing sales that would have happened anyway.
Search Engine Land identifies these two approaches as frequently discussed as though they compete, but they're actually complementary. Attribution answers which channels touched your customers. Incrementality answers which channels changed customer behavior. Using both together stops you from mistaking last-click luck for marketing effectiveness.
Most marketing teams treat attribution as the default because it's been available longer and requires less rigor to execute. Incrementality testing takes more setup and discipline. But that discipline is where real ROI clarity lives. The winners are the ones who measure both, identify the gap, and reallocate ruthlessly toward channels that actually move the needle.
Attribution assigns credit to marketing touchpoints a customer saw before converting. Incrementality asks whether your marketing caused a conversion that wouldn't have happened without it. Attribution says which channel touched them; incrementality says which channel actually changed their behavior. According to Search Engine Land, they use different forms of evidence and answer very different questions about marketing performance.
Attribution only shows which channels got credit for conversions that happened, not whether those conversions were caused by your spending. A customer who was already going to buy anyway still counts in attribution reports, but that's wasted budget. You need incrementality to identify conversions your marketing actually drove versus ones that would have occurred regardless.
Both matter, but for different reasons. Attribution tells you where your customers came from; incrementality tells you where your real ROI is. A channel with high attribution credit might have low incrementality, meaning you're paying for credit rather than actual customer acquisition. Search Engine Land notes they are frequently discussed as competing lenses, but they're actually complementary tools for different decisions.
Start with incrementality testing on your largest ad spend categories, typically paid search and social. Run controlled tests where you pause spend in some regions or cohorts and measure if conversions drop. That difference is your true incremental lift, independent of attribution. Then compare it to what attribution claims credit for and adjust your budget allocation toward the channels that show real incrementality.