period over period variance in crosstab

[tmccurry]

I am attempting to create a crosstab with the measure broken into size groups on the horizontal axis on top and time periods on the vertical axis.  I would like to get period over period variance for each size group.  I created a data item using nested IF-statements called "Segment Group" to break the measure into size groups.  I then created a data item called "Measure Variance" using "running-difference( ( measure) for (segment group) )" to use in the crosstab to attempt to get the period over period variance.  When I do this, the output gives me a total variance for that period just in the first column and leaves the rest of the columns blank, rather than giving me a variance for each "segment group" as I wish.  Any ideas on this problem I'm having? Thanks in advance!