comparative-judgement/lib/pearson.js

Comparative Judgement Algorithms

function correlation(p1, p2) {

  var n = p1.length;

  if (n === 0) return 0;

  var sum1 = 0;
  for (var i = 0; i < n; i++) sum1 += p1[i];

  var sum2 = 0;
  for (i= 0; i < n; i++) sum2 += p2[i];

  var sum1Sq = 0;
  for (i = 0; i < n; i++) {
    sum1Sq += Math.pow(p1[i], 2);
  }

  var sum2Sq = 0;
  for (i = 0; i < n; i++) {
    sum2Sq += Math.pow(p2[i], 2);
  }

  var pSum = 0;
  for (i = 0; i < n; i++) {
    pSum += p1[i] * p2[i];
  }

  var num = pSum - (sum1 * sum2 / n);
  var den = Math.sqrt((sum1Sq - Math.pow(sum1, 2) / n) *
      (sum2Sq - Math.pow(sum2, 2) / n));

  if (den === 0) return 0;

  return num / den;
}

module.exports = {
  correlation: correlation,
};