[R] Drawing the regression line and the 95% confidence intervals

[David L Carlson]

Something like this?

# Compute the prediction limits and get their range to set ylim=
plim <- predict(LinearModel.1, interval = "prediction")
rnge <- c(min(plim[ , 2]), max(plim[ , 3]))
plot(GDP.per.head, fitted(LinearModel.1),ylim=rnge) 

# As before
devlm1<-lm(fitted(LinearModel.1)~GDP.per.head) 
abline(devlm1) 
conflm1<-confint(devlm1) 
abline(coef=conflm1[,1],lty=2) 
abline(coef=conflm1[,2],lty=2) 

# Plot the prediction limits
segments(GDP.per.head, plim[ , 2], GDP.per.head, plim[ , 3], col="gray")

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352


-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Cade, Brian
Sent: Wednesday, May 6, 2015 2:22 PM
To: varin sacha
Cc: R-help Mailing List
Subject: Re: [R] Drawing the regression line and the 95% confidence intervals

The prediction intervals are likely to be much wider than the confidence
intervals so you will need to be sure you scale the yaxis limits large
enough to see them.

Brian

Brian S. Cade, PhD

U. S. Geological Survey
Fort Collins Science Center
2150 Centre Ave., Bldg. C
Fort Collins, CO  80526-8818

email:  cadeb at usgs.gov <brian_cade at usgs.gov>
tel:  970 226-9326


On Wed, May 6, 2015 at 12:59 PM, varin sacha <varinsacha at yahoo.fr> wrote:

> Dear Jim,
>
> I really thank you lots, it perfectly works !
> The reproducible example is below.
>
> Last thing : I can easily get the predictions intervals but I don't get to
> draw them.
> If I want to draw on the same graph (the one I already have the confidence
> intervals) the prediction intervals. I have tried the abline function
> without success. How can I do ?
>
> GDP.per.head=c(600,560,340,560,580,300,570,900,680,290,590,340)
> Quality.score=c(4.5,6.5,6,4.5,7,3,9,10,12.5,6.5,7,9)
> Competitivness.score=c(1000,1200,1400,700,680,1010,340,560,690,500,690,460)
> LinearModel.1=lm(GDP.per.head ~ Quality.score + Competitivness.score)
>
> plot(GDP.per.head, fitted(LinearModel.1),ylim=c(200,800))
> devlm1<-lm(fitted(LinearModel.1)~GDP.per.head)
> abline(devlm1)
> conflm1<-confint(devlm1)
> abline(coef=conflm1[,1],lty=2)
> abline(coef=conflm1[,2],lty=2)
> predict(LinearModel.1, interval = "prediction")
>
> Many thanks once more for your help.
> Sacha
>
>
> ----- Mail original -----
> De : Jim Lemon <drjimlemon at gmail.com>
> À : varin sacha <varinsacha at yahoo.fr>
> Cc : R-help Mailing List <r-help at r-project.org>
> Envoyé le : Mercredi 6 mai 2015 1h02
> Objet : Re: [R] Drawing the regression line and the 95% confidence
> intervals
>
> Hi Sacha,
> The line you have requested is off the plot. The following will
> produce what I think you are asking, but I cannot speak for whether it
> means anything sensible.
>
> plot(GDP.per.head, fitted(LinearModel.1),ylim=c(200,800))
> devlm1<-lm(fitted(LinearModel.1)~GDP.per.head)
> abline(devlm1)
> conflm1<-confint(devlm1)
> abline(coef=conflm1[,1],lty=2)
> abline(coef=conflm1[,2],lty=2)
>
> Jim
>
>
>
> On Wed, May 6, 2015 at 8:01 AM, varin sacha <varinsacha at yahoo.fr> wrote:
> > Hi, Dear R-helpers,
> >
> > Here below you will find a reproducible fictitious example working
> except the "abline" function.
> >
> > First thing : I try to draw the regression line (multiple linear
> regression). I try the "abline" function but it does not work. I don't get
> any error message but the straight line does not appear on the scatterplot.
> >
> > Second thing : I try to draw the 95% confidence intervals on the
> regression line. How could I do ?
> >
> > Using abline(0,1), I can of course add a line 45 degrees angle passing
> through the origin (intercept=0 and slope=1), but it is not what I am
> looking for.
> >
> > GDP.per.head=c(600,560,340,560,580,300,570,900,680,290,590,340)
> > Quality.score=c(4.5,6.5,6,4.5,7,3,9,10,12.5,6.5,7,9)
> >
> Competitivness.score=c(1000,1200,1400,700,680,1010,340,560,690,500,690,460)
> > LinearModel.1=lm(GDP.per.head ~ Quality.score + Competitivness.score)
> > plot(GDP.per.head, fitted(LinearModel.1))
> > abline(GDP.per.head, fitted(LinearModel.1))
> >
> > Thanks for your help. Looking forward to reading you.
> >
> > Sacha
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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 at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.

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