stat-lms

Calculate z-scores using LMS method.

What is stat-lms?

stat-lms is a very simple npm package which calculate z-scores with given LMS values.

LMS (lambda-mu-sigma) values represents skewness, median value, and coefficient of variation. With these values, we can calculate z-scores in a skewed (non-symmetric, non-normal) distribution.

For example, birth weight doesn't follow to normal distribution. So, it is not correct to calculate z-score with standard deviation(σ).

How to Use

const statLms = require('stat-lms');
 
/*
 * LMS values for:
 * Full-term (40 weeks and 0 days) born Japanese boy from primiparae. 
 */
const L = 0.725;
const M = 3094.186;
const S = 0.109;
const weightOfMyBaby = 2535;
 
var zScore = statLms.getZScore(weightOfMyBaby, L, M, S);
var percentile = statLms.getPercentile(zScore);
 
console.log(`My baby's weight is ${zScore.toFixed(2)} SD`);
if(percentile < 10){
    console.log("He is light for gestational age!");
}else{
    console.log("He is appropriate for gestational age.");
}

API

getZScore(value, L, M, S)

Calculate z-score for value with using L, M, and S values.

getPercentile(z)

Calculate percentile value corresponding to z-score(z).

For example, +1.29 SD is equivalent to 90%tile. Baby born with larger than 90%tile weight will be called as Heavy for date.

getValueFromZScore(Z, L, M, S)

Calculate value which is corresponding to z-score(Z) using L, M, and S values.

Author information

Programmed by kcrt (TAKAHASHI, Kyohei) http://profile.kcrt.net/

License

Copyright © 2016 kcrt (TAKAHASHI, Kyohei)
Released under the MIT license
http://opensource.org/licenses/mit-license.php

Reference

1. Cole TJ. Fitting Smoothed Centile Curves to Reference Data. J R Stat Soc Ser A (Statistics Soc. 1988;151(3):385. doi:10.2307/2982992.