def deriv(self, p):
        """
        Derivative of CDF link

        Parameters
        ----------
        p : array-like
            mean parameters

        Returns
        -------
        g'(p) : array
            The derivative of CDF transform at `p`

        Notes
        -----
        g'(`p`) = 1./ `dbn`.pdf(`dbn`.ppf(`p`))
        """
        p = self._clean(p)
        return 1. / self.dbn.pdf(self.dbn.ppf(p))