Can You Measure The Incrementality of Out-Of-Home (OOH) Marketing?

Out-of-home (OOH) marketing has always faced a fundamental measurement challenge. While digital channels give you immediate feedback through clicks, conversions, and detailed user journeys, OOH campaigns like billboards, public transit ads, and digital displays operate in what many marketers consider a measurement black box.

But here's the thing: incrementality testing — the practice of using controlled experiments to measure true causal impact — offers a robust solution to this challenge. The key insight? Experiments, not models, reveal causality and establish the ground truth for cross-channel decision-making without requiring pixels or personally identifiable information (PII).

Understanding incrementality in the offline marketing context

Incrementality testing measures the true additional value generated by a marketing activity by comparing what happened with the activity versus what would've happened without it. For OOH campaigns, this means designing experiments that can isolate the impact of a billboard placement or physical activation from all other factors affecting your business. The principle remains constant whether you're testing digital display ads or highway billboards: controlled experiments reveal which tactics are actually driving business outcomes versus simply correlating with them.

Consider a national retailer launching a digital billboard campaign on the New York subway system. Rather than simply observing sales increases during the campaign period and attributing them to this billboard campaign, an incremental approach would involve a Fixed Geo Test, where this exposed region (NYC) is then compared to a synthetic control model constructed from the remaining DMAs in the US — ensuring both groups are otherwise comparable in terms of demographics, historical sales patterns, and competitive dynamics. Then the difference in performance between these groups represents the true incremental impact of the OOH investment.

These tests rely on three key principles: accuracy and precision through proper statistical design, transparency in documenting methodology and confounding factors, and objectivity by pre-committing to success metrics and analysis methods. The strength of incrementation testing lies in its ability to reveal true causality rather than mere correlation — making it the gold standard for marketing measurement across all channels.

Key factors for successful incrementality testing of offline marketing channels

Not all incrementality experiments are created equal, and this principle becomes especially critical when testing offline channels where data collection presents unique challenges. The strength and reliability of any incrementality test depend on three main categories: accuracy and precision, transparency, and objectivity. For offline channels, achieving these standards requires careful experimental design that accounts for the inherent limitations of traditional media measurement.

Accuracy and precision 

Accuracy and precision in OOH testing often rely on geographic experimentation. By measuring sales lift in test markets compared to control markets, the company can quantify the incremental impact with statistical confidence. The precision of this measurement improves with larger sample sizes and longer test durations — though these must be balanced against the cost and opportunity loss of withholding advertising from control markets.

Transparency

Transparency in OOH incrementality testing means clearly documenting the experimental design, selection criteria for test and control groups, and any adjustments made for confounding factors. A furniture retailer testing a holiday billboard campaign might need to account for seasonal patterns, local economic conditions, and competitive promotional activity. By transparently reporting these considerations and their statistical treatment, the experiment's findings become more credible and actionable for decision-making.

Transparency

Objectivity requires removing bias from both the experimental design and the interpretation of results. When a cosmetics brand tests the impact of in-store displays, objectivity means pre-committing to success metrics and analysis methods before seeing results. It also means acknowledging when experiments show that certain offline tactics aren't incremental — even if those tactics have been long-standing parts of the marketing mix.

The continuous nature of offline testing

Incrementality is a continuous practice, not a one-time measurement, and this principle applies equally to OOH campaigns despite their typically longer planning and execution cycles. While a digital campaign can be tested and optimized within days, offline channels require a different rhythm of experimentation that aligns with their natural cadences. The key is maintaining a consistent experimental agenda — recognizing that each test represents a point in time, with always something new to learn and optimize.

Customization for your business context

Incrementality is unique to your business, and brands can't rely on benchmarks or others' tests when evaluating OOH campaigns. What works for one business may not work for another — even within the same industry. A bank's success with local bench ads doesn't predict whether a credit union in the same market will see similar results. Brand awareness levels, competitive positioning, creative quality, target audience characteristics, and the interaction effects with other marketing activities all play a role — so it's best to test for your specific business.

Integration with business operations

Acting on incrementality improves your business — but only when the insights from OOH testing are properly integrated into reporting, goaling, and budget allocation processes. For instance, Jones Road Beauty discovered through a Fixed Geo Test that their digital billboard campaign in New York City generated significant incremental lift in New Orders, though it wasn't as efficient as they'd hoped. This gave me them insights they needed to act strategically — eager to run billboard campaigns in other locales, but with a focus on CPIA in mind.

The bottom line

Incrementality testing absolutely can work with OOH marketing channels — though it requires thoughtful adaptation of experimental principles to the realities of in-person media. The absence of individual-level tracking actually reinforces the value of experimental approaches, as they provide causal evidence without relying on potentially flawed attribution models.

By embracing continuous experimentation, customizing tests to specific business contexts, and integrating findings into operational decision-making, marketers can bring the same rigor to OOH channel measurement that has transformed digital marketing optimization. Then? It's time to make better decisions about your marketing.