[R] Problem of intercept?

peter dalgaard pd@|gd @end|ng |rom gm@||@com
Wed Feb 22 10:59:36 CET 2023

Not sure what you are trying to do here.

The immediate issue is that you are getting 'y' on the RHS, because that is the 1st column in Dataset. So "for (i in 2:3)" might be closer to intention. 

However, a 0/1 regresson with no intercept implies that the mean for the "0" group is zero, and with two regressors that the mean is zero for the (0,0) group. Looking at the data, this is quite clearly not the case.

I suppose you may have intended to fit the models _with_ the intercept and then _ignore_ the intercept for plotting purposes, i.e. lm(y~x11+x12, Dataset)$coef[-1], etc.?

(Also, I suspect that you don't actually have y=7 and y=867 in the dataset.)

> On 21 Feb 2023, at 22:33 , varin sacha via R-help <r-help using r-project.org> wrote:
> Dear R-experts,
> Here below my R code working with quite a few warnings. 
> x11 and x12 are dichotomous variable (0=no and 1=yes). I substract 1 to ignore intercept.
> I would like not to ignore intercept. How to modify my R code because if I just remove -1 it does not work?
> y= c(32,45,65,34,23,43,65,76,87,98,7,867,56,45,65,76,88,34,55,66)
> x11=c(0,1,1,0,0,1,1,1,0,0,1,0,0,1,0,0,1,1,0,1)
> x12=c(0,1,0,1,0,1,1,0,1,1,0,0,1,1,1,0,0,1,0,0)
> Dataset=data.frame(y,x11,x12)
> a=lm(y~x11+x12-1,Dataset)$coef
> b=NULL
> for(i in c(1:2)) {
>   f=formula(paste('y~',names(Dataset)[i],-1))
>   b=c(b,lm(f,Dataset)$coef)
> }
> coef=data.frame(rbind(a,b))
> coef$Model=c('Multi','Single')
> library(reshape2)
> coef.long<-melt(coef,id.vars="Model")
> library(ggplot2)
> ggplot(coef.long,aes(x=variable,y=value,fill=Model))+
>   geom_bar(stat="identity",position="dodge")+
>   scale_fill_discrete(name="Model",
>   labels=c("Multiple", "Simple"))+
>   labs(title =paste('La différences des coefficients
>   entre la régression multiple et simple'),
>   x="Models",y="Coefficient")+
>   coord_flip()
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Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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