Mid-Parental Height Predictor mechanism

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

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