Summary statistics describing the fit.

        Returns
        -------
        df : DataFrame

def summary(self):
        """Summary statistics describing the fit.

        Returns
        -------
        df : DataFrame
        """
        df = pd.DataFrame(index=self.cumulative_hazards_.columns)

        betas, se = self._compute_slopes()
        df["slope(coef)"] = betas
        df["se(slope(coef))"] = se
        return df