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�̫�A�b�\�h�峹���A�|�ݨ�u�i��ʤ�ҡ]�i��v�^�v�o�@�W���A���ʤ������i��ʤ�Ҭ�       LR+ ={ (a/ [a + c]) / (b/[b + d]) } �]�N�O�A���ʤ������ܤ@�ӯf�H�O�f�H���i��ʻP���ܥL�O�@�Ӱ��d�H���i��ʪ���C�P�˦a�A���ʤ������i��ʤ�Ҭ�       LR- = { (c/[a + c]) / (d/[b + d]) }