I have an SSAS cube containing customers and their purchased memberships (let's say magazines).

I want to calculate the retention. I.e. how many customers remain a customer. To do this I specify a set (males, 30yrs, 1 january 2011).

I want to see if this set - identified by a customer number - is still present in the following months.

I named my set MySet2. What I try to do is: sum(measures.amount, [membership].[name].&[X], MySet2, [date].[date].currentmember)

However, the result is incorrect. The number is far to low. I suspect it still tries to account for all the males of 30 years old, but after a year they're not 30 anymore.

What am I missing? I looked at scope and filter, but I'm not sure how to apply it.