What steps would you take to ensure the reliability of your A/B test results?
Instruction: Discuss the process you would follow to validate the outcomes of an A/B test.
Updated
Official answer
Before launch, define eligibility, stable randomization, treatment, primary metric, guardrails, duration and the analysis/monitoring rules. Plan the required independent units for a specified effect and power; there is no “statistically significant sample size” that guarantees a significant result.
Verify assignment and logging with test cases and, when useful, an A/A test. Check that event definitions, attribution windows and denominators agree between variants. Analyze by the planned assignment and account for repeated observations or clusters.
During the test, monitor allocation ratios, missing telemetry, crossovers and operational harm. An unexplained sample-ratio mismatch is a reason to investigate validity, not to remove inconvenient users until counts match. Safety monitoring can justify stopping exposure; statistical claims still need the planned monitoring method.
At analysis, use the prespecified estimator and uncertainty procedure. Report effects, intervals, sample counts, exclusions and guardrails. Label additional segment searches exploratory and account for multiplicity where confirmatory claims are made. A fixed duration does not by itself cover every seasonal pattern or guarantee validity.
Document defects and unresolved uncertainty before recommending a decision. Replicate or repair the measurement process when the evidence does not support the intended interpretation.