Source: https://guthlabs.ai/docs/instruments/mid-parental-height-predictor/mechanism/

instrument mechanism / verified-clean

# Mid-Parental Height Predictor mechanism

The inspectable method record for Mid-Parental Height Predictor, kept separate from implementation and qualification.

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

## Model scope

No division-by-zero hazard exists. The arithmetic formulas pass under the stated centimeter assumptions, but the specification needs explicit unit handling, accepted sex-input semantics, validation constraints, rounding rules, and provenance/interpretation for the ±8.5 cm range.

- The mid-parental formulas are standard when parental heights and constants use the same units: boys = (father + mother + 13 cm) / 2 and girls = (father + mother - 13 cm) / 2.

- The ±8.5 cm spread is a commonly used population estimate, but it is not universal; the source, population, and whether it represents a prediction interval or a clinical target range are unspecified.

## Units and conventions

- The parental heights must be supplied in centimeters for the stated +13, −13, and ±8.5 values to be dimensionally correct.

- If heights are supplied in inches, they must be converted first: inches × 2.54 = centimeters; alternatively, the sex adjustment must be converted to 5.118 inches and the spread to approximately 3.346 inches.

- The output range is assumed to be [predicted height − 8.5 cm, predicted height + 8.5 cm].

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "father_height_cm": 180,
    "mother_height_cm": 165,
    "child_sex": "boy"
  },
  "expected_outputs": {
    "predicted_height_cm": 179,
    "range_cm": {
      "lower": 170.5,
      "upper": 187.5
    }
  },
  "working": "Sum parental heights: 180 + 165 = 345 cm. Add the boy adjustment: 345 + 13 = 358 cm. Divide by 2: 358 / 2 = 179 cm. Range: 179 − 8.5 = 170.5 cm; 179 + 8.5 = 187.5 cm."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The plain arithmetic formulas produce a numeric result for the exactly-zero parental-height boundary instead of inherently rejecting a physically invalid input, and extreme finite JavaScript inputs overflow to Infinity. Unspecified height units also permit materially divergent interpretations.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/mid-parental-height-predictor/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/mid-parental-height-predictor/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/mid-parental-height-predictor/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`