code: def H6(self):
          "Sum average."
          if not hasattr(self, '_H6'):
              self._H6 = ((self.rlevels2 + 2) * self.p_xplusy).sum(1)
          return self._Hf H6(self):
          "Sum average."
          if not hasattr(self, '_H6'):
              self._H6 = ((self.rlevels2 + 2) * self.p_xplusy).sum(1)
          return self._H6
docs: Sum average.