But those two lines are almose identical The difference between i=0.4432, s=104.1688 and i=0.8776,s=108.1313 is almost negligible.
What I see is that abline draws a line with a v.similar slope but intercept is about 90 instead of 0.8776. Try running the example to see what I mean. ronggui <[EMAIL PROTECTED]> wrote:>?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$tF)) is abline(-0.8776,108.1313) ======= 2005-08-03 22:23:57 ÄúÔÚÀ´ÐÅÖÐдµÀ£º======= > > >Dear R users, please can you help me understand the behaviour of abline using >function lm. > >I'm trying to learn linearity over groups. So I make three groups with 10 >values each: > >test=data.frame(cbind( >l=c(rnorm(10,0,30),rnorm(10,100,30),rnorm(10,200,30)), >t = c(rep(0,10), rep(1,10), rep(2,10)) >)) > >when I do: > >plot(test$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]] > >______________________________________________ >[email protected] 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 --------------------------------- [[alternative HTML version deleted]]
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