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How to run A/B tests in media campaigns

Stop making decisions based on guesswork and start making data-driven decisions. Learn how to set up A/B tests that reveal what truly works.

8 min read Updated July 2026

In paid media, opinion holds little weight, and data holds a lot. What you think will work isn't always what does, and the only way to be sure is by testing. A/B testing is the tool that transforms guesswork into evidence-based decisions.

In this guide, you will understand what an A/B test is, what's worth testing, how to set up a valid test, and how to interpret results without falling into traps.

What is A/B testing and why do it?

An A/B test (or split test) involves comparing two versions of something, version A and version B, to discover which generates better results. You show each version to a similar segment of your audience and measure which performs better. The advantage is clear: instead of betting everything on a hunch, you let real user behavior decide. This is how campaigns consistently improve, test after test.

What to test

Almost everything in a campaign can be tested, but some elements tend to have more impact:

  • Creative: image, video, format.
  • Copy: headline, angle, highlighted benefit, call to action.
  • Audience: different segmentations and interests.
  • Offer: conditions, discounts, bonuses.
  • Landing page: where the ad leads.

Start by testing what tends to move the needle the most, typically creative and offer, before refining smaller details.

How to set up a valid test

The most important rule is: test one variable at a time. If you change the creative, copy, and audience all at once, and the result improves, you won't know which change was responsible. By isolating a single variable, you get a clear answer. Additionally, both versions should run simultaneously and under the same conditions, so that external factors (like the day of the week) don't skew the comparison.

How much time and volume does a test need?

A common mistake is ending a test too early, based on too little data. For a reliable result, the test needs sufficient volume (clicks and conversions) and enough time to capture variations in behavior over several days. Making decisions based on very few conversions is like drawing conclusions from a tiny sample: the difference you see might just be luck, not a real pattern.

How to interpret the results

Ultimately, compare the versions based on the metric that matters for your objective (usually CPA, conversions, or ROAS, not just clicks). The key point is confidence: is the difference between A and B large and consistent enough not to be mere chance? If the two versions end up very close, the test might have been inconclusive, and that's perfectly fine. An inconclusive result is also information: it means that element doesn't make as much difference as initially thought.

Common A/B testing mistakes

The most frequent slip-ups: testing too many variables at once (and not knowing what caused the result); ending too early (deciding with insufficient data); looking at the wrong metric (celebrating clicks when the goal is sales); and not documenting learnings (repeating tests already done). Avoiding these errors turns each test into accumulated knowledge, not wasted effort.

Frequently asked questions

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