By Sam Westbrook, Senior Marketing Analyst, January Digital
In today’s marketing landscape, guesswork is expensive. With media budgets under scrutiny and attribution models breaking down amid privacy shifts and platform walled gardens, brands are learning that assuming what marketing works is no longer enough. Proof is now the standard, and incrementality testing offers one of the clearest paths to that proof. But for many brands, the biggest barrier isn’t how to run a test, but knowing where to start.
Moving from guesswork to evidence-based decisions starts with identifying the right channels for incrementality testing and structuring tests that ladder up to business outcomes. Here’s how brands can validate impact and scale smarter:
- Start Where the Dollars Are
If you want impact, start with the tactics that carry the most weight in your media budget. These are your biggest levers and most likely to deliver meaningful insights. Beginning with single-cell geo holdout tests, where you pause a channel in one group of regions and compare results to similar areas where it remains active is recommended. This simple adjustment can give brands a clear read on the incremental impact of that channel.
Once you have a baseline, move to multi-cell tests to compare how channels perform together versus on their own. This helps identify what drives impact and where to shift spend. Retest as budgets scale or strategies evolve to keep insights fresh and actionable. - Group Smarter, Not Smaller
What about channels with lower spend or unproven channels? That’s where grouping becomes useful. Channels like display or smaller influencer buys may not warrant individual geo holdout tests on their own. But when they are grouped by a shared characteristic, such as a funnel stage, they become easier to test and can help uncover the incremental impact of broader tactic categories.
The goal isn’t to test everything at once. It’s to design a testing roadmap that expands over time, building confidence with every wave. - Build Tests Around Budget, Not Just Attribution
Traditional attribution is losing ground fast. Channel-level misattribution, privacy restrictions, and platform-level noise make it harder than ever to trust what your dashboards are saying. Incrementality tests should be grounded in real, attributable business outcomes like total D2C revenue, store foot traffic, or closed business deals – not just media platform metrics.
That also means knowing when and where to test is critical. The best testing opportunities align with:
– Tactics receiving significant upcoming budget allocations
– Channels where exposure can be cleanly turned off or scaled (think YouTube, TikTok, or Meta)
– Seasonal shifts or campaign launches where tactic changes naturally occur - Don’t Stop at the Test: Feed Your Media Mix Models
One of the most underutilized steps in the testing process is what happens after the test ends. Taking causal ROAS outputs from incrementality tests and feeding them directly into their media mix models, like Google’s Meridian, can increase the accuracy of future forecasts and budget scenarios.
This step bridges the gap between tactical insights and long-term planning, allowing brands to operationalize test learnings across their broader measurement ecosystem.
Every brand is under pressure to prove performance, but that proof only comes from clear, defensible testing. By prioritizing high-impact channels, designing practical test structures, and integrating results into your media mix, brands can make smarter decisions with every dollar.
