You run a two-week incrementality test on your YouTube awareness campaign. Results come back showing minimal lift. Your boss says “Cut the YouTube budget—it’s not working.”
Six months later, your branded search volume has plummeted, organic traffic is down, and your conversion campaigns are struggling. But nobody connects it back to that YouTube cut.
Welcome to the biggest lie in marketing measurement: that you can understand long-term effects with short-term tests.
The incrementality test trap every marketer falls for
Your incrementality provider promises scientific precision. “We’ll run a controlled test and tell you exactly what’s working.” Sounds perfect.
Two weeks later, you get a clean report. Some campaigns show lift, others don’t. You make budget decisions based on this “data-driven” approach.
But here’s what that test didn’t capture: the awareness campaign that showed “no lift” is still building mental availability. The YouTube ad that didn’t drive immediate conversions is creating brand recognition that will pay off months later. It may have seemed ineffective, but it’s slowly shifting consideration in your favor.
Your incrementality test measured marketing like it’s a light switch—on or off, working or not. But marketing actually works like compound interest—small effects building over time into massive results.
The time decay reality
Marketing effects don’t just compound—they also decay at different rates. Your Facebook retargeting might have a short, intense impact that fades quickly. Your podcast sponsorship might have a slow burn that builds for months.
Testing these channels the same way is like judging a sprinter and a marathon runner by their first 100 meters. You’ll completely misunderstand what each one does best.
Some of our most successful client campaigns show minimal impact in month one but massive returns by month six. If they’d relied on incrementality testing alone, they would have killed their best performers. That’s not a problem with Prescient.
The fifth law of marketing
Marketing effects happen over time, compound, and need to be looked at continuously. Isolated tests ignore this.
Marketing isn’t math homework where you get immediate feedback. It’s more like working out—the real results show up weeks or months after you put in the work.
Most incrementality tests run for 2–4 weeks because that’s what’s practical and affordable. But marketing effects can take 3–6 months to fully materialize.
The compound effect you’re missing
Think of marketing like planting an orchard. You plant apple trees today, but you won’t see fruit for years. An incrementality test is like checking for apples after two weeks and concluding “trees don’t work.”
We see this pattern much more often than we’d like. A brand will cut awareness spend based on weak incrementality results, then watch their entire funnel slowly deteriorate over the following quarters.
Here’s what actually happens when you run that YouTube campaign:
Week 1–2: Minimal direct conversions (what your test measures)
Month 1: Brand search volume starts ticking up
Month 2: Organic traffic increases as brand awareness grows
Month 3: Conversion campaigns perform better due to warmer audiences
Month 6: Compound effect creates sustainable competitive advantage
Your incrementality test captured week 1–2 and missed everything else.
The continuous measurement advantage
While your competitors are making decisions based on two-week snapshots, brands that understand Law #5 are tracking long-term patterns and compound effects.
They know that marketing measurement isn’t about finding the “winner” in a head-to-head test. It’s about understanding how different channels work together over time to create sustained growth.
This is why Prescient tracks effects continuously rather than in isolated experiments. We can show you how campaigns from three months ago are still driving value today, and how today’s investments will compound into future returns.
Because here’s the truth: the best marketing decisions aren’t based on what worked in the last two weeks. They’re based on understanding how marketing effects build, interact, and compound over time.
Understanding Law #5—that marketing effects happen over time and compound—protects you from short-term thinking, but there’s another timing element that makes measurement even more complex. Because different businesses don’t just have different marketing effects—they have completely different timelines for when those effects show up.
Next week, we’ll explore Law #6 and why your purchase consideration cycle determines everything about how you should measure marketing performance.
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