Override parent method. Obtain list of the terms and their corresponding
        values using "terms" aggregations for the previous time period.

        :returns: a data frame containing terms and their corresponding values

def aggregations(self):
        """
        Override parent method. Obtain list of the terms and their corresponding
        values using "terms" aggregations for the previous time period.

        :returns: a data frame containing terms and their corresponding values
        """

        prev_month_start = get_prev_month(self.end, self.query.interval_)
        self.query.since(prev_month_start)
        self.query.get_terms("author_name")
        return self.query.get_list(dataframe=True)