When does an item DOES NOT show in the weighted Average list?

[Cognos_World]

Hello

While working with the weighted avg, I encountered a data item not getting displayed in the Weighted Avg list in Calc option.
The Weighted avg shows lot of other items, but the one which I want is not showing up.
The item which I want to see is a conditional calculation. I see other items which are conditional calculations in the weighted Avg by in the calc option.
The item for which I want the weighted avg is an enter able field, so there is no concern of circular reference.

Are there any circumstances when the data item may not show up in the weighted avg by list?

Thanks for reading!