Traffic allocation
How much of the eligible traffic enters a test, and how it is divided between the variants.
Also called traffic split
Allocation has two parts: the share of eligible visitors who enter the test at all, and the split between control and variants (50/50, 90/10, or even across several arms). Visitors outside the test see the current site.
An even split detects differences fastest. An uneven split limits the exposure to a risky change, at the cost of a longer test.
A risky checkout change starts with 20% of visitors in the test, split 50/50, then widens to 100% once the guardrails look fine.
Related terms
- BucketingHow a testing tool assigns each visitor to a variant and keeps them there on later visits.
- Sample ratio mismatch (SRM)When the number of visitors in each variant differs from the planned split by more than chance can explain: a sign the test is broken.
- Multi-armed banditA test that shifts traffic toward the better-performing variant while it runs, instead of keeping a fixed split.
- Mutually exclusive testsTests set up so that no visitor is in more than one of them, to keep tests on the same pages from affecting each other.