def _conditional_time_to_event_(self):
        """
        Return a DataFrame, with index equal to survival_function_, that estimates the median
        duration remaining until the death event, given survival up until time t. For example, if an
        individual exists until age 1, their expected life remaining *given they lived to time 1*
        might be 9 years.

        Returns
        -------
        conditional_time_to_: DataFrame
            with index equal to survival_function_

        """
        age = self.survival_function_.index.values[:, None]
        columns = ["%s - Conditional time remaining to event" % self._label]
        return (
            pd.DataFrame(
                qth_survival_times(self.survival_function_[self._label] * 0.5, self.survival_function_)
                .sort_index(ascending=False)
                .values,
                index=self.survival_function_.index,
                columns=columns,
            )
            - age
        )
Return a DataFrame, with index equal to survival_function_, that estimates the median
        duration remaining until the death event, given survival up until time t. For example, if an
        individual exists until age 1, their expected life remaining *given they lived to time 1*
        might be 9 years.

        Returns
        -------
        conditional_time_to_: DataFrame
            with index equal to survival_function_