Variance calculation in crostab report

[kamala]

I am using cognos 10 report studio to create a crosstab report.I am trying to calculate the variance for the same months for 2 different years
eg.2012 Jan value - 2011 Jan value; 2012 Feb value - 2011 Feb value and so on. How do i achieve it ? Thanks.

[tjohnson3050]

This will very depending on how your data model is structured, but basically on your columns you want to have a year data nested on top of the month data item.  Use the member for the year 2011 nested next to a year member for 2012.  Create a third calculation for 2012 - 2011.  Then nest the months level underneath all three.