Hi
r-help-boun...@r-project.org napsal dne 04.02.2009 12:33:57: > > Hei, > I have a formula for a model as follows > lm(TS~log(BodyWt)+log(BodyWt):factor(D). I do not use R for programming > hence I dont understand what is the second covariate in the model > "log(BodyWt):factor(D)". > Where BodyWt = body weight and D = danger index (either 1 or 2). I want to > run the same model in other program. Can anyone explain me what is doing the > : operator and the factor() function. Factor changes D from numeric (1,2) to factor with levels 1 and 2. As a result from lm with such specified model you shall get one intercept and 2 slopes one for level 1 and second for level 2 of D see x<-1:20 A<-sample(1:2, 20, replace=T) y<-10+x*5*(A==1)+x*12*(A==2)+rnorm(20) fit<-lm(y~x+x:factor(A)) plot(x,y) summary(fit) lines(x, 9.38+x*5.07268) lines(x, 9.38+x*5.07268+x*6.98) Regards Petr > > Thanks > -- > View this message in context: http://www.nabble.com/Factor-and-Lm-functions- > tp21828771p21828771.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > 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.