?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 ______________________________________________ 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.
