Hi Try to put your question on stackexchange. Or maybe it is already answered there. I am not an statistical expert but based on common sense (which can be counter intuitive sometimes) I will use ordered factor if I expect influence of tension value on breaks. Anyway I will probably consult more experienced people around or some textbook.
Regards Petr > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of meng > Sent: Thursday, May 23, 2013 4:44 AM > To: Uwe Ligges > Cc: R help > Subject: Re: [R] ordered and unordered variables > > It's not homework. > I met this question during my practical work via R. > The boss is an expert of biology,but he doesn't know statistics.So I > must find the right method to this work. > > > > > > > > > > > > > At 2013-05-22 17:30:34,"Uwe Ligges" <lig...@statistik.tu-dortmund.de> > wrote: > > > > > >On 22.05.2013 07:09, meng wrote: > >> Thanks. > >> > >> > >> As to the data " warpbreaks", if I want to analysis the impact of > tension(L,M,H) on breaks, should I order the tension or not? > > > >No homework questions on this list, please ask your teacher. > > > >Best, > >Uwe Ligges > > > > > > > > > > > >> > >> > >> Many thanks. > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> > >> At 2013-05-21 20:55:18,"David Winsemius" <dwinsem...@comcast.net> > wrote: > >>> > >>> On May 20, 2013, at 10:35 PM, meng wrote: > >>> > >>>> Hi all: > >>>> If the explainary variables are ordinal,the result of regression > is > >>>> different from "unordered variables".But I can't understand the > >>>> result of regression from "ordered variable". > >>>> > >>>> The data is warpbreaks,which belongs to R. > >>>> > >>>> If I use the "unordered variable"(tension):Levels: L M H The > result > >>>> is easy to understand: > >>>> Estimate Std. Error t value Pr(>|t|) > >>>> (Intercept) 36.39 2.80 12.995 < 2e-16 *** > >>>> tensionM -10.00 3.96 -2.525 0.014717 * > >>>> tensionH -14.72 3.96 -3.718 0.000501 *** > >>>> > >>>> If I use the "ordered variable"(tension):Levels: L < M < H I don't > >>>> know how to explain the result: > >>>> Estimate Std. Error t value Pr(>|t|) > >>>> (Intercept) 28.148 1.617 17.410 < 2e-16 *** > >>>> tension.L -10.410 2.800 -3.718 0.000501 *** > >>>> tension.Q 2.155 2.800 0.769 0.445182 > >>>> > >>>> What's "tension.L" and "tension.Q" stands for?And how to explain > the result then? > >>> > >>> Ordered factors are handled by the R regression mechanism with > orthogonal polynomial contrasts: ".L" for linear and ".Q" for > quadratic. If the term had 4 levels there would also have been a ".C" > (cubic) term. Treatment contrasts are used for unordered factors. > Generally one would want to do predictions for explanations of the > results. Trying to explain the individual coefficient values from > polynomial contrasts is similar to and just as unproductive as trying > to explain the individual coefficients involving interaction terms. > >>> > >>> -- > >>> > >>> David Winsemius > >>> Alameda, CA, USA > >>> > >> > >> [[alternative HTML version deleted]] > >> > >> ______________________________________________ > >> 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. > >> > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. ______________________________________________ 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.
