code: def norm_score(self):
          
          cdf = (1.0 + math.erf(self.score / math.sqrt(2.0))) / 2.0
          return 1 - 2*math.fabs(0.5 - cdf)
docs: Return the normalized score.
  
          Equals 1.0 for a z-score of 0, falling to 0.0 for extremely positive
          or negative values.