Hi Matthew: Thank you very much for sinccere reply! You know I have asked such problems for several times,but your answer is the first reply! Thans a lot! I want to know further (1)how to define the threshold? Another words the reason for definition of threshold is what? (2) Is the the range number of colour column is Z statistics? (3) Only after I elevate the thrsehold the two groups comparision reach statstics difference,How to interpret it? Couly you help me again,thanks in advance. All the best! Nancy Li