2013/11/6 Michael Friendly <frien...@yorku.ca>: > On 11/4/2013 10:45 AM, Sergio Fonda wrote: >> >> Hi, >> I'm not able to get information about the following question: >> >> is the variables standardization a default option in manova() (stats >> package)? >> Or if you want to compare variables with different units or scales and >> rather different variances, you have to previously standardize the >> variables ? >> > > If you mean the response variables, manova() does not require equal > variances and does not standardize. > > > -- > Michael Friendly Email: friendly AT yorku DOT ca > Professor, Psychology Dept. & Chair, Quantitative Methods > York University Voice: 416 736-2100 x66249 Fax: 416 736-5814 > 4700 Keele Street Web: http://www.datavis.ca > Toronto, ONT M3J 1P3 CANADA
Hi Michael, thank you for your reply. However, your remark was not so clear to me so I attach a short script I tried to launch. The comparison between results got from MANOVA() call with the non-standardized and standardized version of the same data frame, convinced me that it is not necessary to standardize data before calling MANOVA. The only difference you get is in the residuals values, of course. Could you kindly confirm my conclusion? All the best, Sergio Fonda ______________________ set.seed(1234) # non- standardized series x1 = rnorm(n=10, mean=50, sd=11) x2 = rnorm(n=10, mean=93, sd=23) x1 = rnorm(n=10, mean=217, sd=52) fact= rep(1:2,20) glob1=data.frame(cbind(x1,x2,x3,fact)) fitta1=manova(cbind(x1,x2,x3)~fact, data=glob1) fitta1.wilks=summary(fitta1, test="Wilks") summary.aov(fitta1) #after standardization x.stand=scale(glob1[,-4]) glob2=data.frame(x.stand,fact) fitta2=manova(cbind(x1,x2,x3)~fact, data=glob2) fitta2.wilks=summary(fitta2, test="Wilks") summary.aov(fitta2) -- Sergio Fonda Associate Professor of Bioengineering Department of Life Sciences University of Modena and Reggio Emilia Modena, Italy ______________________________________________ R-help@r-project.org mailing list 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.
