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...iterature where it is defined as: alpha = 1 / N * sum over( yi - yi,pred,CV) Well it is somehow similar to the RSS for R2 and the PRESS for Q2. But this delta value increases with increasing R2 for the same fitted model I assumend that an error-value would sink with a better fit. So what is the mathmetical equation that lies behind this delta value? Best regards for your help, Markus --------------------------------- [[alternative HTML version deleted]]

...to R. What it lacks are class libraries implementing statistical procedures. I do maintain that those really are not that hard, once you have the matrix and math libraries. My experience with S and R goes way back to the days of blue book S version 3. S called out to C code to handle matrix and mathmetical stuff, but used S code itself to glue it all together in a somewhat object-oriented way. K> I could say "well, given an environment that could interface to C, K> building a GUI on top of that is not really that hard", but that K> would be incredible naive as well....