Split Testing (or A/B Testing)
Split testing, also known as A/B testing, is an experiment where two or more versions of an email are sent to different segments of recipients to determine which performs better.
Split testing (A/B testing) compares variants of an email to see which performs better on a chosen metric.
Definition and examples
Split testing, or A/B testing, is a method used to optimize email performance by comparing two or more variations of an email against each other. Elements such as subject lines, call-to-action buttons, images, copy length or sending times can be tested. The test group is divided into segments, each receiving a different version, and metrics like open rate, click-through rate and conversions are measured to identify the most effective variant. This statistical approach removes guesswork from email marketing decisions by providing concrete data about what resonates best with your audience.
Why it matters
It matters because testing helps teams improve with evidence instead of taste or internal debate. Small wins in subject lines, copy, timing, or layout compound over time.
How to set up A/B tests
Use statistical calculators to determine minimum audience size. Typical split: 50/50 for two variants, adjust for multiple variants. Reserve portion of list for winner rollout (e.g., test 20%, rollout to remaining 80%). Account for list growth and churn during test period.
Common mistakes
A common mistake is making the term sound more complicated than it is in practice. The clearest explanation is usually the most useful one.
Related terms
Key takeaways
A/B testing removes guesswork from email marketing by providing statistical evidence of what works
Test one variable at a time with sufficient sample sizes to achieve reliable results
Focus on high-impact elements like subject lines, CTAs, and sending times for maximum improvement