SELECT
	[Measures].[Thing Count]  ON 0,
	YTD([Effective Date].[Year-Week].[Week].[2013 Week 6]) ON 1
FROM 
	[Cube]

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

Sum(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]

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]