• Try this also...

    With Member [Measures].[Thing Count YTD] As

    AGGREGATE(YTD([Effective Date].[Year-Week].CurrentMember)

    , [Measures].[Thing Count] )

    SELECT

    [Measures].[Thing Count YTD] ON 0,

    [Effective Date].[Year-Week].[Week].[2013 Week 6] ON 1

    FROM

    [Cube]

    This keeps whatever it is you are counting from being double counted.

    ----------------------------------------------------