Thank you Joris,
I'll have a look into the commands you sent me. They look convincing. I hope my students will also see them in a positive way (although I can force them to pretend that they have a positive attitude)!
Dr. Iasonas Lamprianou
Assistant Professor (Educational Research and Evaluation)
Department of Education Sciences
European University-Cyprus
P.O. Box 22006
1516 Nicosia
Cyprus
Tel.: +357-22-713178
Fax: +357-22-590539
Honorary Research Fellow
Department of Education
The University of Manchester
Oxford Road, Manchester M13 9PL, UK
Tel. 0044 161 275 3485
iasonas.lamprianou@manchester.ac.uk
--- On Thu, 3/6/10, Joris Meys wrote:
From: Joris Meys
Subject: Re: [R] ordinal variables
To: "Iasonas Lamprianou"
Cc: r-help@r-project.org
Date: Thursday, 3 June, 2010, 14:35
see ?factor and ?as.factor. On ordered factors you can technically do a spearman without problem, apart from the fact that a spearman test by definition cannot give exact p-values with ties present.
x <- sample(c("a","b","c","d","e"),100,replace=T)
y <- sample(c("a","b","c","d","e"),100,replace=T)
x.ordered <- factor(x,levels=c("e","b","a","d","c"),ordered=T)
x.ordered
y.ordered <- factor(y,levels=c("e","b","a","d","c"),ordered=T)
y.ordered
cor.test(x.ordered,y.ordered,method="spearman")
require(pspearman)
spearman.test(x.ordered,y.ordered)
R commander has some menu options to deal with factors. R commander also provides a scripting window. Please do your students a favor, and show them how to use those commands.
Cheers
Joris
On Thu, Jun 3, 2010 at 2:25 PM, Iasonas Lamprianou wrote:
Dear colleagues,
I teach statistics using SPSS. I want to use R instead. I hit on one problem and I need some quick advice. When I want to work with ordinal variables, in SPSS I can compute the median or create a barchart or compute a spearman correlation with no problems. In R, if I "read" the ordinal variable as numeric, then I cannot do a barplot because I miss the category names. If I read the variables as characters, then I cannot run a spearman. How can I read a variable as numeric, still have the chance to assign value labels, and be able to get table of frequencies etc? I want to be able to do all these things in R commander. My students will probable be scared away if I try anything else other than R commander (just writing commands will not make them happy).
I hope I am not asking for too much. Hopefully there is a way
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Joris Meys
Statistical Consultant
Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control
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