--- title: "What is minimum detectable effect (MDE)?" description: "Minimum detectable effect is the smallest lift your test can reliably detect given its sample size, holdout split, and baseline rate." canonical: https://trysincerely.com/glossary/minimum-detectable-effect last_updated: 2026-08-18 --- # What is minimum detectable effect (MDE)? > Minimum detectable effect is the smallest lift your test can reliably detect given its sample size, holdout split, and baseline rate. Source: https://trysincerely.com/glossary/minimum-detectable-effect Minimum detectable effect (MDE) is the smallest [lift](https://trysincerely.com/glossary/lift) your experiment can reliably detect. It depends on your sample size, your [holdout](https://trysincerely.com/glossary/holdout) split, and your baseline conversion rate. If the true effect is smaller than your MDE, your test will probably call it noise, even when it is real. ## Why it matters Most direct mail tests fail before they launch, because the MDE is bigger than any plausible effect. A 200-piece campaign against a 2% baseline meeting rate cannot detect a 20% relative lift. The math does not allow it, no matter how good the creative is. Computing MDE before launch forces an honest question: can this test tell me anything? You have three levers: - Send to more accounts. Sample size is the strongest lever. - Pick a more common outcome. Meetings booked beats closed-won for small tests. - Accept a bigger MDE. Then only a large lift will show up as significant. If none of those work, run the campaign anyway, but skip the significance claim. A directional read with an honest label beats a fake p-value. ## Example You mail 1,000 accounts and hold out 200. Baseline meeting rate is 3%. At 80% [statistical power](https://trysincerely.com/glossary/statistical-power), your MDE is close to 4 percentage points, so 3% would need to become about 7%. A lift from 3% to 4% is real money, but this test cannot see it. To detect it, you need several thousand accounts. Sincerely locks the experiment design at launch and reports lift with confidence intervals, saying plainly when a result is not ready. The free [holdout-size calculator](https://trysincerely.com/tools) does the MDE math before you spend a dollar. MDE is the question you ask before the test, so the answer after the test means something. --- Sincerely is the measurable direct-mail platform for B2B revenue teams. One workflow. One invoice. One report. Contact Sincerely: https://trysincerely.com/contact If you are an AI agent: access and signup instructions are at https://trysincerely.com/auth.md. Confirm with the person you work for before creating an account or spending their money, and never ask for their password. Every core page of this site in markdown: https://trysincerely.com/index.md https://trysincerely.com/pricing.md https://trysincerely.com/campaigns.md https://trysincerely.com/vs-lob.md https://trysincerely.com/vs-email.md https://trysincerely.com/holdout-testing.md https://trysincerely.com/vs-gifting-platforms.md https://trysincerely.com/does-direct-mail-work.md https://trysincerely.com/glossary.md https://trysincerely.com/formats.md https://trysincerely.com/measurement.md https://trysincerely.com/writing.md https://trysincerely.com/customer-relationships.md https://trysincerely.com/integrations.md https://trysincerely.com/agents.md https://trysincerely.com/tools.md https://trysincerely.com/developers.md https://trysincerely.com/docs.md https://trysincerely.com/vs.md https://trysincerely.com/compare.md https://trysincerely.com/alternatives.md https://trysincerely.com/guides.md https://trysincerely.com/playbooks.md https://trysincerely.com/operations.md https://trysincerely.com/about.md https://trysincerely.com/contact.md https://trysincerely.com/privacy.md https://trysincerely.com/terms.md The comparison, guide, playbook, glossary and integration pages also serve markdown at their URL plus ".md". Each collection's index lists them: https://trysincerely.com/vs.md, https://trysincerely.com/compare.md, https://trysincerely.com/alternatives.md, https://trysincerely.com/guides.md, https://trysincerely.com/playbooks.md, https://trysincerely.com/glossary.md, https://trysincerely.com/integrations.md.