1. What is the LMS Method?

The LMS method is a statistical technique for constructing growth references. It models the distribution of a measurement (like BMI) in terms of its median (M), coefficient of variation (S), and power in the Box-Cox transformation (L) needed to make the distribution normal.

2. How Does the Calculator Work?

The calculator uses the LMS formula:

Where:

• \( BMI \) — Body Mass Index (kg/m²)
• \( M \) — Median BMI for age and sex (kg/m²)
• \( L \) — Box-Cox power (unitless)
• \( S \) — Coefficient of variation (unitless)
• \( \Phi \) — Standard normal cumulative distribution

Explanation: The LMS method transforms BMI measurements to follow a normal distribution, allowing calculation of exact percentiles.

3. Importance of BMI Percentile

Details: BMI percentiles are particularly important in pediatrics to assess growth patterns and identify potential weight problems in children and adolescents.

4. Using the Calculator

Tips: Enter BMI in kg/m², the appropriate M, L, and S values from growth charts for the specific age, sex, and population group. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: Where can I find LMS parameters (M, L, S) for my population?
A: These are typically published in growth reference studies for specific populations (e.g., CDC growth charts, WHO standards).

Q2: What is a normal BMI percentile range?
A: For children, 5th-85th percentile is considered healthy weight, 85th-95th overweight, and ≥95th obese.

Q3: Why use percentiles rather than absolute BMI values for children?
A: Children's BMI naturally changes with age, so percentiles account for normal growth patterns.

Q4: How accurate is this method?
A: Very accurate when using appropriate population-specific LMS parameters, but less so for extreme values.

Q5: Can this be used for adults?
A: While possible, BMI percentiles are primarily used for children. Adults typically use absolute BMI categories.