The concordance score (also known as the c-index) of the fit.  The c-index is a generalization of the ROC AUC
        to survival data, including censorships.

        For this purpose, the ``score_`` is a measure of the predictive accuracy of the fitted model
        onto the training dataset. It's analogous to the R^2 in linear models.

def score_(self):
        """
        The concordance score (also known as the c-index) of the fit.  The c-index is a generalization of the ROC AUC
        to survival data, including censorships.

        For this purpose, the ``score_`` is a measure of the predictive accuracy of the fitted model
        onto the training dataset. It's analogous to the R^2 in linear models.

        """
        # pylint: disable=access-member-before-definition
        if hasattr(self, "_predicted_hazards_"):
            self._concordance_score_ = concordance_index(self.durations, -self._predicted_hazards_, self.event_observed)
            del self._predicted_hazards_
            return self._concordance_score_
        return self._concordance_score_