protected function sortByScore(Identification $a, Identification $b)
    {
        if (is_null($this->scoreKey)) {
            throw new \BadMethodCallException('The key to sort on must be defined using SetScoreKey() prior to sorting.');
        }
        
        if ($a->getScore($this->scoreKey) == $b->getScore($this->scoreKey)) {
            return 0;
        }
        
        return $a->getScore($this->scoreKey) > $b->getScore($this->scoreKey) ? $this->returnTrue : $this->returnFalse;
    }