code: def css(self):
          
          return (self.table[0, 0] * self.table[1, 1] - self.table[0, 1] * self.table[1, 0]) / \
                 ((self.table[0, 0] + self.table[0, 1]) * (self.table[1, 0] + self.table[1, 1]))
docs: Clayton Skill Score (ad - bc)/((a+b)(c+d))