Expected Lift
The most likely improvement of one variant over another, accounting for uncertainty.
What is Expected Lift?
Expected Lift is the average (expected) relative improvement of Variant B over Variant A. It tells you how much better B is likely to be.
For example, an expected lift of +15% means B is expected to have a 15% higher conversion rate than A.
How It's Calculated
Expected lift is calculated by taking many samples from the posterior distributions of both variants and computing the average relative difference.
Expected Lift = E[(B - A) / A]
Interpreting Expected Lift
- Positive lift: B converts better than A
- Negative lift: A converts better than B
- Near zero: Variants perform similarly
Expected Lift vs Observed Lift
The observed lift is simply the difference in conversion rates you see in your data. The expected lift accounts for uncertainty and gives you a better estimate of the true difference.
With small samples, observed lift can be misleading. Expected lift is more reliable.