On Sun, 2010-01-24 at 16:28 -0500, hellen lee wrote: > Hi, all > > I have a question on mgcv and ns. Now I want to compare the results from > glm, gam and ns. Take a simple model y~x for example. > > glm1 = glm(y~x, data=data1) > gam1 = gam(y~s(x), data=data1) > ns1 = glm(y~ns(x),data=data1) > > In order to confirm the result from glm1 is consistent to those from gam1 > and ns1, I want to define degree=1 in mgcv and ns. I am wondering if there > is somebody can give me some suggestions? I appreciate.
require(mgcv) require(splines) data(airquality) m1 <- glm(Ozone ~ Wind, data = airquality) m2 <- gam(Ozone ~ Wind, data = airquality) m3 <- glm(Ozone ~ ns(Wind, df = 1), data = airquality) For gam, I don't think you can set a smooth to be linear, which is what I interpret degree = 1 to be (I also don't know where you get degree = 1 from, this isn't anything to do with ns() in package splines). So we just don't specify that Wind be a smoother in the GAM --- not sure if that is what you wanted? Compare the fits using say summary: e.g. summary(m1); summary(m2) Also, from the above, note that these are all linear models (as opposed to generalised) and would be fitted more efficiently using lm(): m4 <- lm(Ozone ~ Wind, data = airquality) m5 <- lm(Ozone ~ ns(Wind, df = 1), data = airquality) > all.equal(fitted(m1), fitted(m2)) [1] TRUE > all.equal(fitted(m1), fitted(m3)) [1] TRUE > all.equal(fitted(m1), fitted(m4)) [1] TRUE > all.equal(fitted(m1), fitted(m5)) [1] TRUE HTH G > > Hellen > > [[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. -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ 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.
