What is Incrementality Testing?

Incrementality testing is a method used by marketers to measure the true causal impact of a campaign or channel by comparing results between a test group (exposed to the campaign) and a control group (not exposed). It answers a critical question: Did this marketing actually drive more conversions—or would they have happened anyway?

Unlike attribution models that divide credit across touchpoints, incrementality testing isolates lift—the extra value your marketing creates.

Why Incrementality Testing Matters

Attribution tells you what happened. Incrementality tells you what mattered.

In a landscape where conversion paths are messy, attribution data is limited, and performance channels often overlap, incrementality testing helps marketers:

• Prove causal impact of campaigns

• Avoid wasting budget on non-incremental tactics

• Make confident decisions about where to scale or cut spend

It’s especially useful for channels like paid social, influencers, CTV, and affiliate—where attribution data can be noisy or inflated.

How Incrementality Testing Works

A typical test looks like this:

1. Split audience into a control group (no exposure) and a test group (exposed to your campaign).

2. Run your campaign for a set period of time.

3. Measure the difference in conversion or revenue between the two groups.

That difference is your incremental lift—the true value the campaign created.

This can be done through:

• Geo holdouts (e.g. show ads in NY, hold out CA)

• Platform-native tools (like Meta’s Conversion Lift or Google’s Ghost Ads)

• Custom experiments using split testing or first-party data

Common Use Cases for Incrementality Testing

• Validate influencer or podcast ROI when last-click shows weak performance

• Test the true value of retargeting ads—do they convert or just claim credit?

• Measure affiliate program cannibalization

• Prove the upper-funnel impact of CTV, display, or direct mail

Why Incrementality Alone Isn’t Enough

While powerful, incrementality testing has real-world tradeoffs:

• Expensive to run across many channels or cohorts

• Slow to deliver results (weeks or months)

• Requires large audiences for statistical significance

• Not always feasible for small brands or low-volume campaigns

It’s best used strategically—not as your only measurement method.

Why Fairing Helps

Fairing augments incrementality testing by delivering real-time, zero-party data straight from your customers.

• Ask: “How did you hear about us?” immediately post-purchase

• Identify lift across non-clickable channels like podcasts, CTV, and influencer

• Spot trends in customer awareness before test results finalize

• Validate campaign impact with qualitative context from real buyers

Fairing gives you continuous signal between incrementality tests—and can even surface which channels are worth testing next.

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