What is a consequence of not planning ahead before running a live A/B test?

• A. The experiment may impact the performance of the existing campaign
• B. The data will be irrelevant
• C. The test results will be perfect
• D. The test will definitely fail

Answer: (A)

Not planning ahead for a live A/B test can lead to unintended effects on your existing campaigns because the test runs on real traffic. Without a plan, you might allocate or divert budget, impressions, or clicks in ways that change how the current campaign performs. This contamination makes it hard to tell whether any observed differences come from the variant itself or from how the test was run, and it can waste spend or skew results. A clean, planned test specifies traffic splits, duration, sample size for significance, and a rollback strategy to protect the existing campaign.

The other options aren’t as accurate: data isn’t automatically irrelevant just because you didn’t plan; no test yields perfect results; and while poor planning can cause problems, it doesn’t guaranteedly mean the test will fail.