“Incrementality isn’t technically a word—yet it’s both important and mysterious,” said Elizabeth Marsten, vice president of commerce media at Tinuiti, noting that the rapid rise of retail media makes mastering the metric critical.

US retail media spend will reach $60.81 billion in 2025—adding roughly $29.2 billion in new ad dollars, more growth than Meta and Alphabet will see combined, according to EMARKETER’s forecasts. At the same time, 71% of advertisers now rank incrementality as the most important KPI for their retail media investments, an Association of National Advertisers (ANA) survey found.

In this Q&A, Marsten shares how to turn that priority into action. She explains how marketers can tell true incremental sales from halo effects, pick the right measurement tools, and build a flexible framework for an AI-driven future.

Q: How does Tinuiti define incrementality today—and why is it so important to retail media strategy?

Marsten: I learned something funny recently—incrementality isn’t technically a word. Yet, it’s both important and mysterious. At Tinuiti, we approach incrementality in two distinct ways. First, through measurable platforms like Amazon Marketing Cloud, which provides relatively straightforward incrementality measurement within Amazon’s ecosystem. Second, across the broader retail media landscape, where incrementality serves more as an ideal goal and directional metric rather than a precise measurement.

Q: Why is it getting harder to know what’s working in retail media and how is Tinuiti helping marketers make sense of it all?

Marsten: The proliferation of retail media networks (RMNs), mismatched measurement across platforms, varying RMN maturity levels and custom retailer metrics have made clarity harder for brands and Tinuiti. We use a couple of tools to organize the chaos, such as incremental return on ad spending (iROAS) in platforms like Skai for RMNs and our proprietary measurement software, BlissPoint, across the digital landscape.

Q: What signals help you understand what’s really driving results in performance?

Marsten: Topline revenue is a good indicator. If there are sales overall, low product returns, and more product orders, that’s a solid indicator that something is working. New-to-brand (NTB) is a favorite. It’s a far better indicator of reach and incremental sales than ROAS and eliminates doubt on customer acquisition techniques.

While NTB metrics have become a go-to for measuring incrementality—it’s only measuring the first time a customer shopped that brand within that marketplace. It’s not reflective of a true NTB customer. But, if a brand can incorporate their own customer data and compare it to the customer who purchased within a RMN; then they can get a truer sense of which customers are actually new to the brand.

Q: How do you balance customization and scale when applying incrementality across multiple retail platforms and clients?

Marsten: We’ve found a practical balance by using Amazon Marketing Cloud as our gold standard for incrementality measurement—they’ve built a tool that shows what’s actually driving new sales in their walled garden and a bit beyond. For other RMNs, we adjust our approach based on what data they make available. Sometimes that means using Skai to connect the dots across several retailers.

Other times we use BlissPoint to fill in the gaps across channels like search, social and programmatic. The key is being consistent about what we’re trying to measure—new customers and sales that wouldn’t have happened otherwise—while being flexible about how we get there on each platform. It’s not perfect, but it gives brands a much clearer picture of what’s working across their retail mix.

Q: What’s next for incrementality—and how are both teams preparing for the future of retail media measurement?

Marsten: What’s next? More AI software with unique measurement promises. It’s been a total avalanche. We’ve had to develop foundational frameworks to evaluate the RMN technologies available, including software maturity, data portability, visibility, and measurement standards, against global institutions like the Interactive Advertising Bureau and the Media Rating Council to ensure we are all speaking the same language.

Translate strategy into action with a results-driven approach to Amazon, commerce media, and commerce operations. Find out how at Tinuiti.com.