Thanks very much Jari, I appreciate your guidance. I trust R very much, the only thing I can do is to dig up the methodology behind the SPSS result (and of course behind the correspondence analysis itself). Regards, am
Jari Oksanen wrote: > > Artem Mariupol <artem.mariupol <at> gmail.com> writes: > >> >> Hello, >> >> I am new to R and I have a question about the difference between >> correspondence analysis in R and SPSS. >> This is the input table I am working with (4 products and 18 attributes): >> >> > mytable >> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 >> 1 15 11 20 4 14 7 1 2 1 4 12 12 17 19 11 20 9 10 >> 2 19 18 14 14 16 4 14 11 11 15 22 19 22 16 21 19 15 16 >> 3 16 13 10 9 15 4 10 7 11 13 18 17 14 14 16 16 13 11 >> 4 21 18 16 14 20 6 12 14 14 17 23 20 19 18 21 18 19 18 >> >> I found the function corresp() in the package MASS, but the results are >> different from the output in SPSS. Also, I don't understand the >> coordinates; >> in the biplot I cannot find a -2 limit for example from the first product >> on >> any of the x axes. >> > At a quick look, there is nothing strange in the result. Have you > contacted SPSS > and asked them to explain their deviant results? > > It seems that biplot.correspondence is undocumented. However, it has > argument > 'type' which defaults to "symmetric", other alternative being "rows" and > "columns". Intelligent guess is that this selects the scaling of row and > column > scores, and type="symmetric" scales both. By selecting type="columns", > only > columns are scaled and the -2 value for a row will be displayed (which > proves > that the guess was correct). > > I don't have a clue how SPSS scales results, but I guess that the > differences in > the results may be due to different scalings. Function corresp gives you > weighted orthonormal row and column scores, but scales these in the plot > like > specified. It may be that SPSS does the scaling already in the printout > (and > does not give you the choice of type?). Another possible source of > difference is > that corresp gives you "canonical correlations" whereas some other program > or > function may give you their squares, a.k.a. eigenvalues. Moreover, the > sign is > arbitrary so that negative and positive scores may be switched between > programs. > > I hope this helps, > > Jari Oksanen > > ______________________________________________ > [email protected] 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. > > -- View this message in context: http://www.nabble.com/correspondence-analysis-tf3876129.html#a10997356 Sent from the R help mailing list archive at Nabble.com. ______________________________________________ [email protected] 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.
