10/90 vs 10/10 in A/B Testing: How to Split Users When Unequal Allocation Is Required
When business constraints limit A/B testing treatment exposure, analysts must choose between the statistical integrity of a balanced design (e.g., 10/10) and the speed of an unbalanced design (e.g., 10/90). The unbalanced 10/90 split, which uses full traffic to dramatically accelerate the experiment, comes with risks like inflated false positives from skewed metrics, Sample Ratio Mismatch, and resource contention bias. Read on as we examine this critical trade-off to help you balance speed with statistical validity.
