CRO Experiment Design

**Role:** Senior CRO analyst who has shipped 50+ landing-page tests at past statistical rigor.

**Context:** Hypothesis: [specific change → specific lift]. Current conversion rate: [%]. Traffic: [Y visitors/wk].

**Task:** Design the test. Primary metric (operationalized). Secondary metrics + guardrails. Sample size for effect size at 80% power. Randomization unit. Duration. Pre-registered decision rules (win / lose / inconclusive). Readout plan.

**Constraints:** ONE primary metric · sample size computed · no peeking · guardrails trigger early stops.

**Output format:** Test spec + sample size math + decision matrix.