From: ronggui <0034058_at_fudan.edu.cn>

Date: Thu 04 Aug 2005 - 00:39:34 EST

...

*>
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Deparment of Sociology

Fudan University

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Aug 04 00:47:57 2005

Date: Thu 04 Aug 2005 - 00:39:34 EST

>?abline

and you can see

...

'reg' is a regression object which contains 'reg$coef'. If it is

of length 1 then the value is taken to be the slope of a line through the origin, otherwise, the first 2 values are taken to be the intercept and slope.

...

and

*> plot(test$l~test$t)
*

> abline(lm(test$l~test$t))

> (lm(test$l~test$t))

Call:

lm(formula = test$l ~ test$t)

Coefficients:

(Intercept) test$t 0.4432 104.1688

> test$tF=factor(test$t)

*> plot(test$l~test$tF)
**> abline(lm(test$l~test$tF))
**> (lm(test$l~test$tF))
*

Call:

lm(formula = test$l ~ test$tF)

Coefficients:

(Intercept) test$tF1 test$tF2 -0.8776 108.1313 208.3376 when test$tF is factor,these are 3 coef and the first two are used to drow the line,with Intercept = -0.8776 and slope= 108.1313 ,and abline(lm(test$l~test$tF)) is abline(-0.8776,108.1313)

- 2005-08-03 22:23:57 您在来信中写道：=======

> > >Dear R users, please can you help me understand the behaviour of abline using function lm. > >I'm trying to learn linearity over groups. So I make three groups with 10 values each: > >test=data.frame(cbind( >l=c(rnorm(10,0,30),rnorm(10,100,30),rnorm(10,200,30)), >t = c(rep(0,10), rep(1,10), rep(2,10)) >)) > >when I do: > >plot(test$l~test$t) >abline(lm(test$l~test$t)) > > >the abline is a straight line through the centre of the points of each of the groups. > >If, however, I factorise the groups (in order to do e.g. anova analysis) and then plot the data > >test$tF=factor(test$t) >plot(test$l~test$tF) >abline(lm(test$l~test$tF)) > > >the abline is now shifted up and to the left of where I would expect the line to go (through the centre of the points of each of the groups). > >If there is a simple explanation, could someone tell me it? >

> > >--------------------------------- >To help you stay safe and secure online, we've developed the all new Yahoo! Security Centre. > [[alternative HTML version deleted]] > >______________________________________________ >R-help@stat.math.ethz.ch mailing list >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

- = = = = = = = = = = = = = = = = = = =

2005-08-03

Deparment of Sociology

Fudan University

Blog:http://sociology.yculblog.com

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Aug 04 00:47:57 2005

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