Crosstab average not ignoring nulls

[aks12]

I have a simple crosstab in Report Studio that looks at a measure for months throughout the year across a few intervals. I have a calculated member at the bottom of my crosstab that creates an average for each column. My problem is that Cognos is treating nulls as 0 and including them in the average calculation and is giving the incorrect average results as seen below. For example, the average for Int1, Int2, and Int3 should be 25, 20 and 15. Does anybody know how to fix this?

[b]       Int0 Int1 Int2 Int3[/b] 
[b]Jan[/b]      10   10   10   10 
[b]Feb[/b]      20   20   20   20
[b]Mar[/b]      30   40   30     
[b]Apr[/b]      40   30
[b]May[/b]      50 
[b]Average[/b]  30   20   12    6

 

[aks12]

I solved this by first creating a calculation that creates a count of the months if my measure > 0. Then I created a calculation that summed the measure in each column. Then it was easy to create an average calcuation like [Count]/[Total].