Incrementality case study
Measuring for incrementality makes Dunelm’s Facebook Ads 90% more effective
Dunelm and Crealytics ran a randomized controlled experiment to compare the attribution system ROAS against incremental impact - with surprising results.
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01 Introduction
Incrementality: theory vs practice
The explanation for this paradox is that even digitally savvy organizations struggle to bridge the gap between theory and practice.
This case study shows how a home furnishings retailer and Crealytics have bridged this gap together by measuring and improving the incremental return of Facebook campaigns.
About Dunelm


There is more than meets the eye; any attribution model is likely to over- or undervalue the incremental value of any campaign.
But alas, most attribution reports are wrong and can even cause harm. The numbers reported to marketers do not show the true financial impact of marketing channels and campaigns. To understand true causal impact, incrementality testing is needed.
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In classic holdout tests, a test group gets to see ads while a control group does not. Comparing the resulting buying behavior of both cohorts delivers first estimates on how much revenue would be lost without advertising in that channel. This is what we define as the incremental impact.
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Knowing incremental campaign value is only the first step. The final goal is to act on insights by re-allocating budgets to maximize the incremental return on ad spend (3).
02 The Challenge
Exploring new ways to move the needle
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Prospecting campaigns to target people with no prior visit to the retailer’s website
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Retargeting campaigns to advertise to past website visitors
Dunelm and Crealytics had two hypotheses in mind:
But before any execution, these counterintuitive tactics needed proof in data.
03 The approach
Retargeting vs Prospecting
What is Facebook's Conversion Lift tool?
Conversion lift compares the actions of real people in randomized test and control groups to measure the additional online, offline or mobile app business driven by Facebook, Instagram and Audience Network ads.
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During the test, budgets for both segments were balanced to achieve the same nominal ROAS according to client’s Multitouch Attribution. Under a traditional valuation, both campaigns delivered the same advertising efficiency.
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The remarketing campaigns incremental ROAS was only 44%, while the acquisition campaigns drove a staggering incremental ROAS of 298%. In other words, the multitouch attribution model underestimated its true value by two-thirds!
04 The Results
A 5.7x higher return from prospecting vs retargeting
As a result, the Dunelm’s incremental Facebook ROAS increased by +90%, driving nearly twice as much impact for every advertising dollar. While incrementality optimization can seem daunting at first, it is worth implementing as it is one of the biggest levers to really drive business impact.
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