'Observed agreement between two coders on all items.'

def Ao(self, cA, cB):

    data = self._grouped_data(u'item', (x for x in self.data if (x[u'coder'] in (cA, cB))))
    ret = (sum((self.agr(cA, cB, item, item_data) for (item, item_data) in data)) / len(self.I))
    log.debug(u'Observed    agreement    between    %s    and    %s:    %f', cA, cB, ret)
    return ret
