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NNT
—
ARD —
Waiting for inputs
Formula
ARD = EER − CER · NNT = ⌈100 ÷ ARD⌉
Trial reference
Event rates
Result wording
Enter control and experimental event rates — or pick a trial preset.
Worked example — CER 8.3% · EER 50% → ARD 41.7 pp · NNT 3 (Cormio 2011, 1 month)
Educational only — not medical advice. Disclaimer.
How to use this
- CER — % of people with the event in the control / placebo arm.
- EER — % with the event in the experimental arm.
- ARD — EER minus CER, in percentage points.
- NNT — ceiling of 1 ÷ ARD (as a proportion). Always pair with a time horizon.
- Presets — published dichotomous figures from our guides. Small-n caveats stay attached.
What this does not do
Continuous outcomes (mean IIEF change, hair count per cm², kg lost) do not get an NNT. Relative risk or odds ratio without baseline rates are not enough. Observational studies are out of scope. If the experimental arm does worse, use NNH framing — this tool flags that case instead of inventing a benefit NNT.