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testland/experiment-results-interpreter
Use when an A/B test result is read for a ship decision, especially off a dashboard, a small sample or many metrics. Computes significance per metric with multiple-comparison correction, reads confidence intervals, checks novelty, interactions, Simpson's paradox, guardrails and stop-early rules.
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significance-anti-patterns.mdreferences/
Significance-check anti-patterns
Each row maps a common analysis mistake to the step that prevents it.
| Anti-pattern | Why it fails | Fix |
|---|---|---|
| Peeking and stopping at first significance | Inflates false-positive rate dramatically. | Pre-register stop date OR use sequential testing (Step 7). |
| Single metric only | Misses regressions in secondary metrics (revenue down even though completion up). | 5-10 metrics including guardrails (Step 1). |
| No multiple-comparisons correction | 10 metrics × α=0.05 = 40% chance of false positive somewhere. | FDR / Bonferroni (Step 3). |
| Ship based on practical significance without statistical | Random variance gets shipped as "lift." | Both required (Step 5). |
| Ship based on statistical significance without practical | 0.1% lift at N=10M ships; not worth maintenance burden. | MDE per metric (Step 5). |
| Welch's t-test on heavy-tailed metrics (revenue) | Test invalid; conclusion wrong. | Mann-Whitney U for non-normal metrics (Step 2). |
| Ignoring guardrail metrics (support tickets, churn, refund rate) | Ship something that breaks downstream. | Always include guardrails (Step 6 example). |