code: def chisq_red(self):
          
          if self._chisq_red is None:
              self._chisq_red = chisquare(self.y_unweighted.transpose(), _np.dot(self.X_unweighted, self.beta), self.y_error, ddof=3, verbose=False)
          return self._chisq_red
docs: The reduced chi-square of the linear least squares