Hi, I am using a data called Rail in the nlme package. The data contains two variables: Rail and Travel.>RailGrouped Data: travel ~ 1 | Rail Rail travel 1 1 55 2 1 53 3 1 54 4 2 26 5 2 37 6 2 32 7 3 78 8 3 91 9 3 85 10 4 92 11 4 100 12 4 96 13 5 49 14 5 51 15 5 50 16 6 80 17 6 85 18 6 83>Rail$Rail >[1] 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 >Levels: 2 < 5 < 1 < 6 < 3 < 4Then I used the contrasts function as:>contrasts(Rail$Rail)And it returns with some strange continuous values: .L .Q .C ^4 ^5 [1,] -0.5976143 0.5455447 -0.3726780 0.1889822 -0.06299408 [2,] -0.3585686 -0.1091089 0.5217492 -0.5669467 0.31497039 [3,] -0.1195229 -0.4364358 0.2981424 0.3779645 -0.62994079 [4,] 0.1195229 -0.4364358 -0.2981424 0.3779645 0.62994079 [5,] 0.3585686 -0.1091089 -0.5217492 -0.5669467 -0.31497039 [6,] 0.5976143 0.5455447 0.3726780 0.1889822 0.06299408 I am expecting to see 0s and 1s in the contrast, but it may be due to the order of the factor levels for Rail variable? Best, Jing [[alternative HTML version deleted]]
Rail is an ordered factor. ?ordered for details. Default contrasts for an ordered factor are orthogonal polynomials. See: stat.ethz.ch/pipermail/r-help/2007-January/123268.html and ats.ucla.edu/stat/r/library/contrast_coding.htm#ORTHOGONAL -- Bert On Fri, Feb 8, 2013 at 1:36 PM, jing tang <gimmytang at gmail.com> wrote:> Hi, > I am using a data called Rail in the nlme package. The data contains two > variables: Rail and Travel. >>Rail > Grouped Data: travel ~ 1 | Rail > Rail travel > 1 1 55 > 2 1 53 > 3 1 54 > 4 2 26 > 5 2 37 > 6 2 32 > 7 3 78 > 8 3 91 > 9 3 85 > 10 4 92 > 11 4 100 > 12 4 96 > 13 5 49 > 14 5 51 > 15 5 50 > 16 6 80 > 17 6 85 > 18 6 83 >>Rail$Rail >>[1] 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 >>Levels: 2 < 5 < 1 < 6 < 3 < 4 > > Then I used the contrasts function as: >>contrasts(Rail$Rail) > And it returns with some strange continuous values: > .L .Q .C ^4 ^5 > [1,] -0.5976143 0.5455447 -0.3726780 0.1889822 -0.06299408 > [2,] -0.3585686 -0.1091089 0.5217492 -0.5669467 0.31497039 > [3,] -0.1195229 -0.4364358 0.2981424 0.3779645 -0.62994079 > [4,] 0.1195229 -0.4364358 -0.2981424 0.3779645 0.62994079 > [5,] 0.3585686 -0.1091089 -0.5217492 -0.5669467 -0.31497039 > [6,] 0.5976143 0.5455447 0.3726780 0.1889822 0.06299408 > > I am expecting to see 0s and 1s in the contrast, but it may be due to the > order of the factor levels for Rail variable? > > Best, > Jing > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list > stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.-- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm