I found the question really confusing as well, but see below. On Thu, Jul 28, 2011 at 11:42 AM, David Winsemius <dwinsem...@comcast.net> wrote: > > On Jul 28, 2011, at 9:13 AM, m.fen...@libero.it wrote: > >> >> Dear R users, >> I'd like to known your opinion about a problem with anova.lmRob() of >> "Robust" package that occurs when I run a lmRob() regression on my dataset. >> I check my univariate model by single object anova as anova(lmRob(y~x)). >> If I compare my model with the null model (y~1), I must obtain the same >> results, >> but not for my data. >> Is it possible? >> >> My example: >> >> x<-c(rep(0,8),rep(1,8),rep(2,7)) >> >> y<-c(1,0.6,-0.8,0.7,1.6,-0.2,-1.2,-3.8,-1.8,-2.6,-1.7,-2.1,-0.3,-1.4,1.4,-0.3,-0.3,0.5,0.4,-0.9,-1.6,0.4,0.4) >> library(robust) >> lmR<-lmRob(y~factor(x)) >> anova(lmR) >> lmR0<-lmRob(y~1) >> anova(lmR,lmR0) >> >> If I run the code omitting the factor() (then treating "x" as continuous), >> the results are the same.. >> > > I do not get the same results with that code. And the code does not appear > to track your description, since the second model does not have an "x" term > in it. Even when I create the model that it sounded as though you would have > written, namely lmR0 <- lmRob(y ~ x), it is clearly _not_ the same result. > >> coef(lmR) > (Intercept) factor(x)1 factor(x)2 > 0.2428571 -1.3432007 -0.4000000 >> coef(lmR0) > (Intercept) x > -0.509524217 0.005820355 >> >> What is the explanation of these different results? > > Since you didn't post your results and since your complaint was that they > are "the same", it's hard to know what you are talking about.
I think the question is why lm1 <- lm(y ~ factor(x)) lm0 <- lm(y ~ 1) anova(lm1) anova(lm0, lm1) gives the same result, but lmR<-lmRob(y~factor(x)) lmR0<-lmRob(y~1) anova(lmR) anova(lmR,lmR0) does not. I don't know the answer, but I think it is an interesting question. Best, Ista > > -- > David Winsemius, MD > West Hartford, CT > > ______________________________________________ > 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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.
