chi-squared-test

Chi-Squared Test

This package provides a small function for calculating a chi-squared test on a given dataset. Given an observed set of frequencies observations, an expected set of frequencies expectations, and the number of degrees of freedom reduced in the measurement, calculates the probability that the observations came from the same probability distribution.

For example, let's check a die for fairness:

var chiSquaredTest = require('chai-squared-test');

// We expect a fair die
var expected = [2, 2, 2, 2, 2, 2];

// Looks pretty unfair...
var observed = [6, 3, 3, 0, 0, 0];

// Reduction in degrees of freedom is 1, since knowing 5 categories determines the 6th
var reduction = 1;

var probability = chiSquaredTest(observed, expected, reduction);
// Gives 0.010362, which indicates that it's unlikely the die is fair 

// However, something a little more likely
observed = [2, 2, 4, 4, 2, 2];
probability = chiSquaredTest(observed, expected, reduction);
// Gives back 0.549416, which is indicates that they did come from the same distribution (by most statistical standards)