Hi all, I have the following data called "data1". After fitting the ancova model with different slopes and intercepts for each region, I calculated the regression coefficients and the corresponding standard error. The standard error (for intercept or for slope) are all the same for different regions. Is there something wrong? I know the SE is related to (X^T X)^-1, where X is design matrix. So does this happen whenever each factor level has the same set of values for "week"? Thanks. Hanna
> mod <- lm(response ~ region*week, data1)> tmp <- coef(summary(mod))> res <- > matrix(NA, 5,4)> res[1,1:2] <- tmp[1,1:2]> res[2:5,1] <- tmp[1,1]+tmp[2:5,1]> > res[2:5,2] <- sqrt(tmp[2:5,2]^2-tmp[1,2]^2)> res[1,3:4] <- tmp[6,1:2]> > res[2:5,3] <- tmp[6,1]+tmp[7:10,1]> res[2:5,4] <- > sqrt(tmp[7:10,2]^2-tmp[6,2]^2) > colnames(res) <- c("intercept", "intercept SE", "slope", "slope SE")> > rownames(res) <- letters[1:5]> res intercept intercept SE slope > slope SE a 0.18404464 0.08976301 -0.018629310 0.01385073 b 0.17605666 0.08976301 -0.022393789 0.01385073 c 0.16754130 0.08976301 -0.022367770 0.01385073 d 0.12554452 0.08976301 -0.017464385 0.01385073 e 0.06153256 0.08976301 0.007714685 0.01385073 > data1 week region response 5 3 c 0.057325067 6 6 c 0.066723632 7 9 c -0.025317808 12 3 d 0.024692613 13 6 d 0.021761492 14 9 d -0.099820335 19 3 c 0.119559235 20 6 c -0.054456186 21 9 c 0.078811180 26 3 d 0.091667189 27 6 d -0.053400777 28 9 d 0.090754363 33 3 c 0.163818085 34 6 c 0.008959741 35 9 c -0.115410852 40 3 d 0.193920693 41 6 d -0.087738914 42 9 d 0.004987542 47 3 a 0.121332285 48 6 a -0.020202707 49 9 a 0.037295785 54 3 b 0.214304603 55 6 b -0.052346480 56 9 b 0.082501222 61 3 a 0.053540767 62 6 a -0.019182819 63 9 a -0.057629113 68 3 b 0.068592791 69 6 b -0.123298216 70 9 b -0.230671818 75 3 a 0.330741562 76 6 a 0.013902905 77 9 a 0.190620360 82 3 b 0.151002874 83 6 b 0.086177696 84 9 b 0.178982656 89 3 e 0.062974799 90 6 e 0.062035391 91 9 e 0.206200831 96 3 e 0.123102197 97 6 e 0.040181790 98 9 e 0.121332285 103 3 e 0.147557564 104 6 e 0.062035391 105 9 e 0.144965770 [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.