I am needing some expertise with regard to the S-Plus command lmRobMM and its R counterpart rlm(formula,data,method="MM") I have used lmRobMM(formula,data) in S-Plus on the Stackloss data and obtained for my residuals 6.217777 1.150717 6.427946 8.174019 -0.6713005 -1.248641 -0.4236203 0.5763797 -1.057899 0.3593823 11 12 13 14 15 16 17 18 19 20 0.9629239 0.4732042 -2.506497 -1.346176 1.344408 0.1432279 -0.3729551 0.09646618 0.5861859 1.934193 21 -8.629863 (Intercept) V1 V2 V3 -37.65246 0.7976856 0.5773405 -0.06706018 but when I use rlm(formula,data,method="MM") in R my residuals are 1 2 3 4 5 6 2.82002948 -2.29288550 3.78605126 7.23168396 -1.60941126 -2.18886365 7 8 9 10 11 12 -1.09082616 -0.09082616 -1.43350203 -0.32664493 0.68958988 0.15612729 13 14 15 16 17 18 -3.10081497 -1.43820259 2.20031311 0.86156818 -0.29869392 0.49171093 19 20 21 1.02517352 1.61796106 -10.50956979 (Intercept) VAR00001 VAR00002 VAR00003 -41.5230433 0.9388404 0.5794524 -0.1129150 I am very worried by this discrepancy what have I done wrong? I read in R:Robust Fitting of Linear Models: MM estimation is M-Estimation with Tukey's biweight initialized by a specific S-estimator and so I alter my S-Plus code to ct<-lmRobMM.robust.control(weight=c("Optimal","Bisquare")) fit<-lmRobMM(formula=V4~V1+V2+V3,data=data, robust.control=ct) and obtain for my residuals 1 2 3 4 5 6 7 8 9 10 11 12 13 14 6.132346 1.061665 6.342018 8.212728 -0.7022119 -1.244742 -0.3631877 0.6368123 -1.001597 0.2162886 0.8524152 0.3242646 -2.64235 -1.407392 15 16 17 18 19 20 21 1.338706 0.1266635 -0.4053969 0.08936822 0.6175189 1.894162 -8.820719 (Intercept) V1 V2 V3 -37.35298 0.8107863 0.5425301 -0.07068073 then I try ct<-lmRobMM.robust.control(weight=c("Bisquare","Bisquare")) fit<-lmRobMM(formula=V4~V1+V2+V3,data=data, robust.control=ct) and obtain 1 2 3 4 5 6 7 8 9 10 11 12 13 14 5.954287 0.880977 6.206231 8.16344 -0.7473658 -1.291963 -0.3966992 0.6033008 -1.020411 0.1894031 0.8491936 0.3204805 -2.663977 -1.402163 15 16 17 18 19 20 21 1.392297 0.1723669 -0.3985709 0.1145995 0.6433127 1.882605 -8.908035 (Intercept) V1 V2 V3 -37.56484 0.8178879 0.5445969 -0.07331006 no matter what I try I cannot reproduce my R-fit? thank you for the time you spend with this query cheers Daniel