Thank you both Bert and David, for the quick reply. I will look further into this.
With regards, Tal ----------------Contact Details:------------------------------------------------------- Contact me: tal.gal...@gmail.com | 972-52-7275845 Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) | www.r-statistics.com (English) ---------------------------------------------------------------------------------------------- On Fri, Dec 2, 2011 at 5:08 PM, Bert Gunter <gunter.ber...@gene.com> wrote: > Maybe should have explicitly said: > > > C(ordered(1:5)) > [1] 1 2 3 4 5 > attr(,"contrasts") > ordered > contr.poly > Levels: 1 < 2 < 3 < 4 < 5 > > -- Bert > > On Fri, Dec 2, 2011 at 7:06 AM, Bert Gunter <bgun...@gene.com> wrote: > > ?ordered > > ?C > > ?contr.poly > > > > If you don't know what polynomial contrasts are, consult any good > > linear models text. MASS has a good, though a bit terse, section on > > this. > > > > -- Bert > > > > On Fri, Dec 2, 2011 at 6:51 AM, Tal Galili <tal.gal...@gmail.com> wrote: > >> Hello dear all, > >> > >> I am unable to understand why when I run the following three lines: > >> > >> set.seed(4254) > >>> a <- data.frame(y = rnorm(40), x=ordered(sample(1:5, 40, T))) > >>> summary(lm(y ~ x, a)) > >> > >> > >> The output I get includes factor levels which are not relevant to what > I am > >> actually using: > >> > >> Call: > >>> lm(formula = y ~ x, data = a) > >>> Residuals: > >>> Min 1Q Median 3Q Max > >>> -1.4096 -0.6400 -0.1244 0.5886 2.1891 > >>> Coefficients: > >>> Estimate Std. Error t value Pr(>|t|) > >>> (Intercept) -0.03276 0.15169 -0.216 0.830 > >>> x.L -0.28968 0.33866 -0.855 0.398 > >>> x.Q -0.38813 0.33851 -1.147 0.259 > >>> x.C -0.27183 0.34027 -0.799 0.430 > >>> x^4 0.25993 0.33935 0.766 0.449 > >>> Residual standard error: 0.9564 on 35 degrees of freedom > >>> Multiple R-squared: 0.08571, Adjusted R-squared: -0.01878 > >>> F-statistic: 0.8202 on 4 and 35 DF, p-value: 0.5211 > >> > >> > >> I am guessing that this is having something to do with the contrast > matrix > >> that is used, but this is not clear to me. > >> Can anyone suggest a good read, or an explanation? > >> > >> Thanks. > >> > >> > >> ----------------Contact > >> Details:------------------------------------------------------- > >> Contact me: tal.gal...@gmail.com | 972-52-7275845 > >> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) > | > >> www.r-statistics.com (English) > >> > ---------------------------------------------------------------------------------------------- > >> > >> [[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. > > > > > > > > -- > > > > Bert Gunter > > Genentech Nonclinical Biostatistics > > > > Internal Contact Info: > > Phone: 467-7374 > > Website: > > > http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm > > > > -- > > Bert Gunter > Genentech Nonclinical Biostatistics > > Internal Contact Info: > Phone: 467-7374 > Website: > > http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm > [[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.
