docs: function variance(array) {
    var length = array.length;
  
    if (length === 0) {
      throw new RangeError('Error');
    }
  
    var index = -1;
    var mean = 0;
  
    while (++index < length) {
      mean += array[index] / length;
    }
  
    var result = 0;
  
    for (var i = 0; i < length; i++) {
      result += Math.pow(array[i] - mean, 2);
    }
  
    return 1 / length * result;
  }