Computes the Kruskal-Wallis test for equal medians.

The Kruskal-Wallis rank sum test evaluates for multiple samples the null hypothesis that their medians are identical. The Kruskal-Wallis test is a nonparametric test which does not require the data to be normally distributed.

To carry out the test, the rank sums S_h of the individual groups are calculated. The test statistic is then calculated as

where N denotes the total number of observations and t_{r(i)} are the number of tied observations with rank i.

$ npm install compute-kruskal-test

For use in the browser, use browserify.

var kruskal = require( 'compute-kruskal-test' );

For input arrays a, b, ... holding numeric observations, this function calculates the Kruskal-Wallis rank sums test, which tests the null hypothesis that the medians in all k groups are the same. The function returns an object holding the calculated test statistic K, the pValue of the test and the degrees of freedom (df).

var kruskal = require( 'compute-kruskal-test' );

var x, y, z,
	out,
	table;

// data from Hollander & Wolfe (1973), 116.
x = [2.9, 3.0, 2.5, 2.6, 3.2];
y = [3.8, 2.7, 4.0, 2.4];
z = [2.8, 3.4, 3.7, 2.2, 2.0];

out = kruskal( x, y, z );
/*
{ H: 0.7714,
  df: 2,
  pValue: 0.6799 }
*/

table = out.toString();
/*
Kruskal-Wallis rank sum test.
	null hypothesis: the medians of all groups are the same.
	test statistic: 0.7714
	df: 2
	p-value: 0.68
*/

To run the example code from the top-level application directory,

$ node ./examples/index.js

Unit tests use the Mocha test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

MIT license.

Copyright © 2015. The Compute.io Authors.