I'm pulling my hair out on this one, so hope somebody can help me out. I'm using SPSS 19 on a dataset structured like this (dummy data):
Time1 Time2 Time3 Group ----- ----- ----- ----- 0 2 4 0 0 0 5 1 1 2 7 0 1 3 4 0 etc...
I can easily manually or using SPSS calculate the means for the different follow-ups (Time1, Time2 and Time3) first for Group 0 and then for Group 1.
But then I create a clustered bar chart by choosing 'Clustered bar char', dragging Time1, Time2 and Time3 to the Y-axis, dragging my Group-variable to the X-axis. Which creates a chart like this:
Legend shows my three followups (Time1 etc), X-axis shows my two groups (0 or 1).
While it apparently looks fine and dandy, I can clearly see that the mean values are simply wrong compared to the mean I can calculate myself, or the ones reported when I compare mean using a T-test!
I mean the very last bar shown in the example should show the mean of Time3 for the last Group, right? That's what I'd figure, but the mean is not correct. :(
Is there something basic I just don't understand about the clustered bar charts? Any help or hints are very appreciated.