Running parallel tests

Parallel testing means running multiple A/B tests simultaneously on your website or product. This practice can speed up learning, but it comes with specific requirements to ensure valid results. The key is understanding how multiple tests might interact with each other and what precautions to take. There are 2 main approaches to running parallel tests:

• Section-based testing keeps different tests confined to separate areas of your product — like testing a new onboarding flow while separately testing account settings.
• User-based testing assigns users to specific test groups and ensures they stay in those groups across all tests. Both approaches help prevent test contamination and maintain clear results.

Test interaction effects need careful monitoring. Even with proper separation, combining too many tests can reduce your traffic per variation and make it harder to reach statistical significance. Calculate how your sample size requirements change when running multiple tests. For example, if each test needs 1,000 users to be valid, running four tests means you need enough traffic to maintain those numbers across all variations.^[1]