code: def fallout(self):
          r
          if self._fp + self._tn == 0:
              return float('NaN')
          return self._fp / (self._fp + self._tn)
docs: r"""Return fall-out.
  
          Fall-out is defined as :math:`\frac{fp}{fp + tn}`
  
          AKA false positive rate (FPR)
  
          Cf. https://en.wikipedia.org/wiki/Information_retrieval#Fall-out
  
          Returns
          -------
          float
              The fall-out of the confusion table
  
          Example
          -------
          >>> ct = ConfusionTable(120, 60, 20, 30)
          >>> ct.fallout()
          0.25