abline and linearity over groups
?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$tF)) is abline(-0.8776,108.1313)
======= 2005-08-03 22:23:57 ÂÄÂúÂÔÂÚÂÀ´ÂÃÂÃ…ÂÖÂÃÂôµÂÀ£º=======
Dear R users, please can you help me understand the behaviour of abline using function lm. I'm trying to learn linearity over groups. So I make three groups with 10 values each: test=data.frame(cbind( l=c(rnorm(10,0,30),rnorm(10,100,30),rnorm(10,200,30)), t = c(rep(0,10), rep(1,10), rep(2,10)) )) when I do: plot(test$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]]
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= = = = = = = = = = = = = = = = = = = = 2005-08-03 ------ Deparment of Sociology Fudan University Blog:http://sociology.yculblog.com