Incrementality testing: what is it and how to run lift tests for paid social

Platform reporting is no longer accurate since iOS 14, and traditional attribution models often rely on last click, which is seriously misleading and limits marketers’ understanding of their campaigns’ true performance.

So how can you know your ads are actually working?

The answer is incrementality testing – also known as lift testing – the gold standard for understanding the true value of your marketing.

What is incrementality?

Incrementality is a word that has been on the menu for marketing discussions for years, but is now the main course.

Put simply, imagine you’re filling a glass of water drop by drop. Each drop represents an action in your marketing – ads, emails, social posts. Incrementality is understanding which drops are actually filling the glass and which ones would have happened anyway.

Marketers have been through many versions of what “the truth” is, generally in service of two masters: getting maximum bang for their buck, and justifying investments to the wider organisation. One doesn’t always tie in with the other. We have experienced many versions of the North Star, from Last Click to Multi-Touch to Incrementality – each progressively harder to deliver and justify.

The reason incrementality has become the buzzword is that optimising towards this North Star will give you the best bang for your buck.

Why incrementality matters in marketing

The challenge with modern digital marketing is that customer journeys are rarely linear – and platform reporting doesn’t capture the full picture.

Seeing an ad from a brand makes it statistically more likely that you will click on an ad from that brand months later. Clicking on an ad from a brand makes it more likely that you will select their Google Shopping placement months later. And clicking on a Google Shopping ad from a brand makes it more likely you will click on a TikTok ad months later.

But platforms only optimise and report on the short-term. They take credit for conversions that may have happened anyway, and they can’t see the cross-channel ripple effects of your spend. This creates a fundamental question: how can you make sure you are investing in the right placements, at the right proportion?

Incrementality should be the North Star of your marketing activity. Without it, you’re making budget decisions based on incomplete – and often misleading – data.

Types of lift tests

There are several types of incrementality tests, each suited to different objectives:

Conversion lift studies measure the direct impact of your ads on conversions such as purchases, sign-ups, or leads. They compare conversion rates between an exposed group and a holdout group to isolate the incremental conversions driven by your ads. Meta’s Conversion Lift tool is one of the most widely used options for running these on paid social.

Brand lift tests measure the impact of your advertising on softer metrics like brand awareness, ad recall, and consideration. These are particularly useful for understanding the value of upper-funnel campaigns that don’t drive immediate conversions but build long-term demand.

Search lift studies measure how your paid social ads influence search behaviour – specifically, whether people exposed to your ads are more likely to search for your brand on Google afterwards. This is one of the most powerful ways to measure the cross-channel impact of your social spend.

Geo-lift tests take a geographic approach, running ads in some regions while holding others back, then comparing performance across locations. These are useful when audience-level holdout tests aren’t feasible.

How Meta conversion lift studies work

Nest has a strong partnership with the marketing science team at Meta, and we implement lift studies across our portfolio of ecommerce clients to understand where and how much they should invest to drive value from paid social.

Meta’s Conversion Lift tool works by randomly splitting your target audience into a test group (who see your ads) and a holdout group (who are prevented from seeing them). After a set test period, Meta compares conversion rates between the two groups to calculate the incremental lift your ads delivered.

The results can be eye-opening. Proving incremental gains can be challenging, but lift studies bridge the gap in understanding. For example, across multiple Nest tests, use of Meta’s Search Lift tool showed how upper-funnel ads directly impact brand search:

• Running Meta awareness ads for a month drove an average of 3,359 incremental branded search visits – a 22.3% search lift
• The same campaigns drove 5,082 incremental non-branded search visits – a 9.4% search lift

This further outlines the impact Meta ads have on Google performance, and the importance of a strong cross-channel approach. Your Facebook and Instagram spend isn’t just driving direct conversions – it’s fuelling your entire acquisition funnel.

Incrementality measurement: best practices

Run tests at the right scale. Lift tests need sufficient audience size and budget to reach statistical significance. Running a test with too small a budget or too short a window will produce unreliable results.

Test one variable at a time. If you’re testing the incrementality of prospecting campaigns, don’t change your retargeting strategy at the same time. Isolate the variable you want to measure.

Account for cross-channel effects. As the data above shows, paid social activity has a measurable impact on search behaviour. Any incrementality measurement framework should consider these cross-platform dynamics, not just the direct conversions reported by each platform.

Test regularly, not once. Incrementality isn’t a fixed number – it changes with seasonality, audience saturation, creative fatigue, and competitive dynamics. Regular testing gives you an up-to-date picture of where your spend is truly driving value.

Make sure your team has the experience. Lift tests are powerful but require careful setup, execution, and interpretation. Poorly configured tests can lead to misleading conclusions that are worse than no test at all.

Start measuring the true value of your ads

If you haven’t run lift tests, you should do so at once to make sure you are making the right investments.

Nest has experience running incrementality tests across our client base of ecommerce brands. We help brands understand where to invest, how much to spend, and which channels are truly driving incremental growth.

If you want to find out the true value of your ads, we can help you. Contact us here.

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