[RsR] robust scatterplot with fits

[Matias Salibian-Barrera]

Hello Pep,

If NPP is the response variable (the "y" variable) and WPROB is the 
explanatory variable (the "x" variable), then you should have used

lmrob(NPP ~ WPROB, data=a)

Also, I recommend you use the latest version of the "robustbase" package

 > install.packages('robustbase')
 > library(robustbase)

There the function for a robust regression fit is called lmrob (not 
lmRob, which is now deprecated).

Finally, based on your plot, you might also want to consider a model 
incorporating log(WPROB), since the relationship does not appear to be 
quite linear to the naked eye.

Hope this helps.

Matias




On 10-10-19 07:32 AM, Pep Serra sat down at the computer and wrote:
>    Dear RsR list members,
>
> I somehow got stuck wth lmRob and I am sure I am missing something and I
> do not know what. It is my first time using robust statistics and I have
> read all your posts and pdfs recommended
>
> I think it is likely to be a newbie question. I ploted two variables and
> the pictures shows a number of outliers that I want to identify given
> that the main trend between those two measurements is positive.
> (although they look like a lot, it is more or less 800 points out of 6000)
>
>
>
>
>
> I used then
>
> robust<-lmRob(WPROB~NPP,data=a)
>
>
> lmRob(formula = WPROB ~ NPP, data = a)
>
> Coefficients:
> (Intercept) NPP
> 499.86274538 -0.00990502
>
> Degrees of freedom: 6002 total; 6000 residual
> Residual standard error: 250.3199
>
> 1) I do not really understand the slope of the regression, why is it
> negative???
>
> then used plot.lmRob(robust) and choose for option 11 (scatter plot with
> fits)
>
>
>
> What is meant to be the x axis (WPROB) turns into the y axis.
> The regression line and the confidence intervals shown have nothing to
> do, of course, with the coefficients retrieved...what am I doing wrong?
>
> Thank you in advance,
>
> pep
>
>
>
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> https://stat.ethz.ch/mailman/listinfo/r-sig-robust


-- 
_____________________________________________________
Matias Salibian-Barrera - Department of Statistics
The University of British Columbia
Phone: (604) 822-3410 - Fax: (604) 822-6960
"The plural of anecdote is not data" (George Stigler?)