Source: https://guthlabs.ai/docs/instruments/nnt-nnh-number-needed-to-treat-harm/

instrument / verified-clean

# NNT/NNH (Number Needed to Treat/Harm)

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/nnt-nnh-number-needed-to-treat-harm/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/nnt-nnh-number-needed-to-treat-harm/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/nnt-nnh-number-needed-to-treat-harm/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/nnt-nnh-number-needed-to-treat-harm/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Biology, Medicine & Pharmacology (educational estimates only — every panel labeled not-medical-advice)

**Tranche**: tranche-5

**Evidence ID**: t5-181

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The educational, not-medical-advice label is appropriate, but the specification needs explicit definitions for RRR/RRI, benefit-versus-harm labeling, percentage-versus-proportion input handling, zero-denominator behavior, and integer rounding before it can be considered complete.

### Formula and scope findings

- ARR=|CER−EER| is correct when CER and EER are event probabilities expressed in the same units.

- NNT=1/ARR is correct mathematically for a beneficial treatment effect, while the same absolute-risk formula yields NNH when EER>CER; the specification does not define this direction-based labeling.

- RRR is listed as an output but no RRR formula is supplied. For benefit, the standard formula is RRR=(CER−EER)/CER=ARR/CER when EER<CER.

- For harm, RRR is not the correct label; the corresponding measure is relative risk increase, RRI=(EER−CER)/CER. The specification does not define whether to output RRI, a negative RRR, or null.

- NNT and NNH are normally reported as positive integers rounded up, but the specification does not state a rounding rule. The raw reciprocal may be fractional.

- The formulas require CER and EER to be probabilities between 0 and 1, or percentages converted consistently before calculation; this constraint is not stated.

### Unit assumptions

- CER and EER are assumed to be event probabilities on the 0 to 1 scale unless explicitly converted from percentages.

- ARR is dimensionless as a probability difference; if rates are entered as percentages, ARR must be converted from percentage points to a proportion before taking its reciprocal.

- RRR and RRI are dimensionless ratios, conventionally reported as percentages after multiplying by 100.

- NNT and NNH are counts and should conventionally be rounded up to the next whole person for reporting.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

Equal control and experimental event rates produce ARR=0, so NNT and NNH require division by zero and are undefined. The specification also lists RRR as an output without defining its formula or sign convention, creating a convention-dependent result.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "CER": 0.2,
    "EER": 0.15
  },
  "expected_outputs": {
    "ARR": 0.05,
    "RRR": 0.25,
    "NNT_raw": 20,
    "NNT_reported": 20,
    "NNH": null
  },
  "working": "ARR=|0.20−0.15|=|0.05|=0.05. Because EER<CER, this is benefit, so RRR=(0.20−0.15)/0.20=0.05/0.20=0.25=25%. NNT=1/0.05=20, so reported NNT=20. NNH is not applicable because the experimental event rate is lower."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`