Hello, I tried to find a fitting forum but did not quiet succeed. The following diagram is an example of something I've been given at work. I try to understand it but fail with that. http://img98.imageshack.us/img98/4770/testwk3.png [Broken] So how do I understand such diagram? The upper black dot comprises all the data in all 4 groups or colours, the second highest black dot assumes two groups? But where's the boundary then: between the light blue and green? What are the boundaries of the third black dot? Basically: how do I understand such diagram? Thanks a lot, H.