[R] Problem with regression line

[David L Carlson]

To expand on Eik Vettorazzi's answer:

Don't use html emails. When the mailing list converts it to plain text, it often re-wraps lines so that your code becomes jumbled.

First, you did not define coeff. You need to add

coeff <- coef(SimpleLinearReg1)

Second, you should use the formula you used for the regression in the plot command or the correct order (plot uses the first variable as the x-axis and the second variable as the y-axis while the formula specification uses the variable on the left of the tilde (~) as the y-axis and the variable on the right of the tilde as the x-axis. Your regression predicts age (response) from blood pressure (explanatory) so abline() assumes age is on the y-axis and blood pressure is on the x-axis, but you reversed that so the line is "plotted", but it is outside the plot window. 

Either change the regression formula to BloodPressure~Age (which makes more sense than predicting age from blood pressure) or change the plot command to plot(BloodPressure, Age, ...) and change the xlab to ylab and ylab to xlab).

----------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77843-4352

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Eik Vettorazzi
Sent: Wednesday, April 18, 2018 9:25 AM
To: CHATTON Anne <Anne.Chatton using hcuge.ch>; r-help using R-project.org
Subject: Re: [R] Problem with regression line

Hi Anne,
I would suggest to change the linear model to lm(BloodPressure~Age), as this model makes more sense in biological means (you would assume that age influences pressure, not vice versa) and also obeys the statistical assumption of weak exogeneity, that age can be measured without error, at least compared to error-prone bp measures.

Cheers

Am 18.04.2018 um 16:07 schrieb Gerrit Eichner:
> Hi, Anne,
> 
> assign Age and Bloodpressure in the correct order to the axes in your 
> call to plot as in:
> 
> plot(y = Age, x = BloodPressure)
> abline(SimpleLinearReg1)
> 
> 
>  Hth  --  Gerrit
> 
> ---------------------------------------------------------------------
> Dr. Gerrit Eichner                   Mathematical Institute, Room 212 
> gerrit.eichner using math.uni-giessen.de   Justus-Liebig-University Giessen
> Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany 
> http://www.uni-giessen.de/eichner
> ---------------------------------------------------------------------
> 
> 
> Am 18.04.2018 um 15:26 schrieb CHATTON Anne via R-help:
>> Hello,
>>
>> I am trying to graph a regression line using the followings:
>>
>> Age <- c(39, 47, 45, 47, 65, 46, 67, 42, 67, 56, 64, 56, 59, 34, 42, 
>> 48, 45, 17, 20, 19, 36, 50, 39, 21, 44, 53, 63, 29, 25, 69) 
>> BloodPressure <- c(144, 220, 138, 145, 162, 142, 170, 124, 158, 154, 
>> 162, 150, 140, 110, 128, 130, 135, 114, 116, 124, 136, 142, 120, 120, 
>> 160, 158, 144, 130, 125, 175) SimpleLinearReg1=lm(Age ~ 
>> BloodPressure)
>> summary(SimpleLinearReg1)
>> eq = paste0("y = ", round(coeff[2],1), "*x ", round(coeff[1],1)) 
>> plot(Age, BloodPressure, pch = 16, cex = 1.3, col = "blue", main = 
>> eq, xlab = "Age (Year)", ylab = "Blood Pressure (mmHg)") 
>> abline(SimpleLinearReg1, col="red")
>> mean(Age)
>> mean(BloodPressure)
>> abline(h=142.53, col="green")
>> abline(v=45.13, col="green")
>>
>> But I cannot get the regression line. Can anybody tell me what's 
>> wrong with the codes ? I would appreciate very much. Thanks for any help.
>>
>> Anne
>>
>>     [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help using 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.
>>
> 
> 

--
Eik Vettorazzi

Department of Medical Biometry and Epidemiology University Medical Center Hamburg-Eppendorf

Martinistrasse 52
building W 34
20246 Hamburg

Phone: +49 (0) 40 7410 - 58243
Fax:   +49 (0) 40 7410 - 57790
Web: www.uke.de/imbe
--

_____________________________________________________________________

Universitätsklinikum Hamburg-Eppendorf; Körperschaft des öffentlichen Rechts; Gerichtsstand: Hamburg | www.uke.de
Vorstandsmitglieder: Prof. Dr. Burkhard Göke (Vorsitzender), Prof. Dr. Dr. Uwe Koch-Gromus, Joachim Prölß, Martina Saurin (komm.) _____________________________________________________________________

SAVE PAPER - THINK BEFORE PRINTING
______________________________________________
R-help using 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.