scope statement on a Hierarchy

Hi,

I have a week by quarter hierarchy (Quarter is parent and week is child) like the following:

  example:     Hierarchy   Measure

                     Q412          blank

                     oct 6          100

                     oct 13         200

I  want to update the parent cell value from blank to some value using the scope statement and do not want to update the child values but when i write scope statement the update happens to all the three cells above. What should i be doing to update only the parent?

Following is the scope statement i wrote which is updating all 3 cells to same value of 20

       SCOPE(MEASUREGROUPMEASURES("ABC"),[DATE].[WEEK BY QTR].[QTR].&[Q412]   );

             this=20;

      END SCOPE;