def pr_ghmean(self):
return ghmean((self.precision(), self.recall()))<EOL>
Return geometric-harmonic mean of precision & recall.

        Iterates between geometric & harmonic means until they converge to
        a single value (rounded to 12 digits)

        Cf. https://en.wikipedia.org/wiki/Geometric-harmonic_mean

        Returns
        -------
        float
            The geometric-harmonic mean of the confusion table's precision &
            recall

        Example
        -------
        >>> ct = ConfusionTable(120, 60, 20, 30)
        >>> ct.pr_ghmean()
        0.8278323841238441