Incrementality
Paid MediaAlso: Incrementality Testing · Incremental Lift
Quick definition
Incrementality is the measure of how many conversions a marketing channel actually caused, rather than simply claimed credit for. It's tested by comparing results with the channel switched on against results with it switched off, usually through a holdout group or geo-based experiment.
How it varies across Australia
Incrementality testing is still rare among mid-market Australian advertisers, more common in enterprise retail and finance where media budgets justify the setup cost. Where it has been run, brand and retargeting spend usually shows the widest gap between attributed credit and actual lift.
See acquisition benchmarks across Australian industries →What it actually means
Imagine turning off your retargeting campaign for two weeks and watching what happens to sales. If nothing changes, that campaign wasn't causing conversions. It was catching people who were going to buy regardless and taking the credit for it. That's the entire idea behind incrementality.
Most businesses run on attribution, which divides credit among the touchpoints a customer encountered before converting. Attribution assumes those touchpoints mattered. Incrementality tests whether they actually did, by comparing a group exposed to the channel against a matched group that wasn't.
This matters most for channels with strong intent-capture behaviour. Branded search, retargeting and email to existing customers all tend to look brilliant on CPA and ROAS reports because they're reaching people who were already close to converting. Incrementality testing routinely finds that a meaningful share of that spend is buying conversions that would have happened without it.
The uncomfortable part is that incrementality often contradicts what the attribution model says, which means the two systems answer different questions and neither replaces the other.
Attribution tells you who claimed the sale. Incrementality tells you whether the sale would have happened anyway.
How to calculate it
Incremental lift = Conversions with the channel on minus conversions with it off
Worked example. You run a two-week geo holdout on retargeting. Regions with the campaign live convert at 1,200 sales. Matched regions with the campaign switched off convert at 1,050 sales. The incremental lift is 150 sales, meaning the campaign only caused 150 of the 1,200 conversions it was credited with.
The Australian context
Australia's smaller population makes geo-based incrementality tests trickier to run cleanly than in the United States, since there are fewer comparable regions to split into test and control without one market bleeding into another through shared media or word of mouth. Businesses here often lean on holdout audience tests instead of geo splits, particularly for email and retargeting where the audience can be randomised directly rather than split by state.
Where people get this wrong
Incrementality vs Attribution
| Incrementality | Attribution | |
|---|---|---|
| What it answers | Did this spend cause the conversion | Who gets credit for the conversion |
| Method | Holdout groups or geo experiments | Rule-based or modelled credit assignment |
| Cost to run | Requires a controlled test period | Runs continuously from existing data |
| Best for | Deciding whether to keep funding a channel | Reporting and day-to-day optimisation |
Related terms
Common questions
How is incrementality testing different from A/B testing?
A/B testing usually compares two versions of a single asset like an ad or a landing page. Incrementality testing compares having a channel switched on against having it switched off entirely, across a holdout audience or region, to measure whether the channel causes conversions at all.
Why would a high-ROAS channel show low incrementality?
ROAS is calculated from attributed conversions, which credit the channel for sales it simply caught rather than caused. Retargeting and branded search often reach people already intending to buy, so the attributed number looks strong while the actual incremental lift is small.
How long does an incrementality test need to run?
Long enough for normal conversion volatility to settle so the lift is statistically clear, typically several weeks depending on your conversion volume. Lower-traffic businesses need longer tests to get a reliable read than high-volume ones.
Do small businesses need incrementality testing?
Not always. It requires enough conversion volume to detect a meaningful difference between test and control groups. Smaller businesses often get more value from simpler holdout checks on their biggest spend channel rather than building a full testing programme.
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About New Rebellion
New Rebellion is a marketing intelligence consultancy. We build tools, score Australian businesses on how their marketing actually performs, and publish Debrief every day. This dictionary is part of how we work in the open.
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