:rtype: list

def group(self):
        """
        :rtype: list
        """
        lowerbound = self.lowerbound
        age_group_list = []
        for age_group in self.et.findall("group"):
            upperbound = age_group.attrib["upperbound"]
            try:
                poppercent = age_group.attrib["poppercent"]
            except KeyError:
                poppercent = None
            age_group_list.append({"lowerbound": lowerbound,
                                   "upperbound": upperbound,
                                   "poppercent": poppercent})
            lowerbound = upperbound
        return age_group_list