I would like to test if a model is bias by grouping residuals into categroies and testing if the mean of the residuals for the group is different from zero. Since I'm a little new to R programming, what is the best way to group residuals, say into n groups over the predicted values. I could use a loop, but I have a feeling that there is a method like symnum that would do the trick. Yes? Jeff. Jeff D. Hamann Hamann, Donald & Associates, Inc. PO Box 1421 Corvallis, Oregon USA 97339-1421 Bus. 541-753-7333 Cell. 541-740-5988 jeff_hamann at hamanndonald.com www.hamanndonald.com -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._