Hi, I apologize this question is not very r-related, but believe many people using R are expertised at or interested to know the answer to the following question. I am having a problem in classification. In bioinformatics study, we always ends with a limited size of samples. While in algorithms, some specific algorithm cannot handle modeling with more than 2 classes problem. For the time being, not considering those limitations, I just have a general question like this: suppose I have a problem for classification, which involves 5 classes. I am wondering if there is a general research comparison on which approach is more accurate: building 5 binary_class models or building one 5-class model (suppose cost (penalty) is same when accuracy is estimated). An extended or more practical question, in bioinformatics, if you do not have many samples but you are having such problem, what approach will you take? thanks, -- Weiwei Shi, Ph.D Research Scientist GeneGO, Inc. "Did you always know?" "No, I did not. But I believed..." ---Matrix III