How to add rolling 12 to this expression?

[#1]

Hi

I have this expression

Sum(Aggr(If(Sum({<KVA = {'DV132'} >} _Flag_KVA) >= 2 and Count({<KVA = {'DV200'} >} P_ID) >=1, 1), P_ID, SurgeryID))

It shows me how many patients that have been coded as DV132 multiple times and also have been coded as DV200 on each Surgery-unit. Now I only want to get the patients that this occurs within the same 12 months period.

I have a master calender and have tried to add this expression without any result.

({<Year=, Month=, PeriodCounter = {">$(=max(PeriodCounter-12))<=$(=max(PeriodCounter))"} >}

Where should I put the Periodcounter expression? Or should I use any other way to solve it?

[giakoum]

This is an optimum way to do it

Calculating rolling n-period totals, averages or other aggregations