Understanding Prediction Error
Why error bands change with maturity—and how to use them with confidence.
- Error changes by stage: highest around PHV.
- Re-test 3–6 months: tighter trends, better confidence.
- Use trends, not labels: guide decisions, avoid pigeonholing.
Understanding Prediction Error in Height Calculations
The Khamis–Roche method is widely used to predict adult height from current measurements (and, optionally, parental heights). Prediction error isn’t static—it changes with maturity. Early in growth, small measuring differences can compound into larger uncertainty; near adult height, error tightens.
Typical Error Ranges by Maturity
| % of Predicted Adult Height | Boys Error | Girls Error | Why it matters |
|---|---|---|---|
| ~70% (pre-puberty) | ±5.0 cm (≈3–4%) | ±4.0 cm (≈3%) | Early predictions are noisier—big growth still to come. |
| ~80–85% (around PHV window) | ±6.0 cm (up to ≈4%) | ±5.0 cm (≈3–4%) | Rapid change = highest uncertainty. Re-test improves stability. |
| ~90–95% (late puberty) | ±2–3 cm (≈1–2%) | ±2.0 cm (≈1%) | Error shrinks as growth slows. |
| >97% (near adult) | ±1–2 cm | ±1 cm | Very precise—minimal growth remaining. |
How to Convert % Error into cm
If a boy is predicted to be 180 cm at adulthood and the error band is 3.5%:
Absolute error (cm) = 0.035 × 180 = 6.3 cm
So his predicted adult height might reasonably fall within ±6.3 cm of the current estimate.
Why Error Changes with Maturity
- Measurement sensitivity: A 3–5 mm difference matters more earlier on.
- Biology: Growth rates accelerate and then decelerate, peaking at PHV (Peak Height Velocity).
- Data density: More consistent re-tests (every 3–6 months) reduce noise and tighten error bands.
Practical Takeaways
- Focus on trends across months, not single points.
- Use error bands to guide decisions (e.g., training load, competition, expectations).
- Results inform development—they don’t label athletes.
- Re-measure carefully: shoes off, tall posture, same time of day where possible.
How MatCalc Uses Error Bands
MatCalc displays maturity context (e.g., % of predicted adult height) alongside the predicted outcomes. Error ranges adjust with maturity so parents and coaches can:
- See where the athlete likely is relative to PHV.
- Judge confidence around the estimate today.
- Plan when to re-test to tighten the band.
Visualising Error by % Adult Height
Spline curves illustrate how percentage error typically varies by maturity stage for boys and girls.