Read an Experiment Without Fooling Yourself
Interpret an A/B test using primary metric, guardrails, and practical significance.
Decide whether to launch a checkout urgency banner. Read tests through significance, practical value, and guardrails. The trap is launching because p=.04 looks green while ignoring cost and harm. Primary result +1.1% checkout conversion, p=.04 The result likely reflects a real treatment difference under the test design. Practical threshold Pre-set launch threshold was +2.0% or $25k/month net The observed lift does not clear the business bar. Guardrail Refund requests +0.8 points and complaints +14% Customer harm moved in the wrong direction. Decision Do not scale; redesign and retest The experiment created learning, not permission to launch. The readout changes from…
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