def series_down(self, column_groups, row_groups=None, value_position=0):
        """
        Return selected slice of a report on a vertical axis

        Parameters
        ----------
        column_groups: string or list
            The selected column to return series from
            If multiple grouping levels a list is used to identify grouping of interest
        row_groups: string, list or None, optional, default None
            Limits rows included in Series to those within specified grouping
        value_position: int, default 0
            Index of value of interest, if only one value included by default will select
            correct value

        Returns
        -------
        series: dict, {label: value, ...}
        """
        static_grouping_key = "groupingsAcross"
        dynamic_grouping_key = "groupingsDown"

        return self._series(column_groups, static_grouping_key, dynamic_grouping_key,
                            dynamic_groups_of_interest=row_groups, value_position=value_position)