MSAS Trimmed Average

Hi,

I have the following table:
OrderNumber varchar(15)
Completed int(1)
Certificate int(1)
ThroughputTime int(4)

With the following data:
OrderNumber Completed Certificate ThroughputTime
00001 1 1 1
00002 1 1 2
00003 1 0 1
00004 1 0 1
00005 0 1 2
00006 0 1 1
00007 0 0 4
00008 0 0 89

I have a dimension:
All Completed
- Completed
- Not Completed

and a dimension:
All Certificate
- No Certificate
- Certificate

I also have a measures:
TptSum which Sums ThroughputTime
TptCount which Counts OrderNumbers
TptAvg which divided TptSum by TptCount

My problem is with the next measure:
In MSAS I created a Cube which shows the measures on the columns and both Completed and Certificate on the rows. The OrderNumber selection is set to "All Ordernumbers". The measures a listed above are displayed exactly as i expect them to do. TptSum gives the sum for the subselection showed on the left. TptCount and TptAvg also show the expected values on their distinct rows.
I can't upload a screenshot but it looks like this:


TptSum TptCount TptAvg
All Certificate All Completed 101 8 12.63
Completed 5 4 1.25
Not Completed 96 4 24.00
No Certificate All Completed 95 4 23.75
Completed 2 2 1.00
Not Completed 93 2 46.50
Certificate All Completed 6 4 1.50
Completed 3 2 1.50
Not Completed 3 2 1.50

So far so good. Each datarow only takes the records that match the criteria at the left.
Now however, To exclude exceptions that have a huge impact on the average I want to create a trimmed average. That is, I want to exclude the top 25% values in my trimmed average measure, which are the 2 records with the highest ThroughputTime, being ordernumber 00007 and 00008 in the "All Certificate" & "All Completed" row, but different in the other rows. I also want the bottom 25% values to be trimmed, which are the 2 records with the lowest ThroughputTime, being ordernumber 00001 and 0003 in the "All Certificate" & "All Completed" row.

I tried a lot of things, but i can't get it working. Somehow all my statements don't take the subselections on the rows into account. Really frustrating.

What I want to achieve is the following:

TptSum TptCount TptAvg TrimmedAvg
All Certificate All Completed 101 8 12.63 1.50 ((2+1+2+1) / 4) (middle 4 records)
Completed 5 4 1.25 1.00 ((1+1) / 2) (middle 2 records)
Not Completed 96 4 24.00 3.00 ((2+4) / 2) (middle 2 records)
No Certificate All Completed 95 4 23.75 2.50 ((1+4) / 2) (middle 2 records)
Completed 2 2 1.00 1.00 ((1+1) / 2) (all 2 records)
Not Completed 93 2 46.50 46.50 ((4+89) / 2) (all 2 records)
Certificate All Completed 6 4 1.50 1.50 ((1+2) / 2) (middle 2 records)
Completed 3 2 1.50 1.50 ((1+2) / 2) (all 2 records)
Not Completed 3 2 1.50 1.50 ((1+2) / 2) (all 2 records)

I hope I describe my problem well... I also hope someone knows a solution. I can also post the things I tried, but I'm afraid that makes it more confusing, because nothing worked ;)

Thanks,

Edward