Message-ID: <24307524.1257180835858.JavaMail.root@elwamui-rustique.atl.sa.earthlink.net>
Date: 2009-11-02T16:53:55Z
From: Peter Flom
Subject: qqplot
David Winsemius <dwinsemius at comcast.net> wrote
>I always assumed that the intercept was zero and the slope = unity.
>
> y <- rt(200, df = 5)
> qqnorm(y); qqline(y, col = 2)
> qqplot(y, rt(300, df = 5))
> abline(0, 1, col="red")
>
Suppose you have the following
x <- rnorm(500)
y <- 500*(x + runif(500, 0,1))
qqplot(x,y)
Then an abline(0,1) will not be useful; it will be an almost horizontal line. But
m1 <- lm(y~x)
abline(coef(m1))
does the trick.
Peter
Peter L. Flom, PhD
Statistical Consultant
Website: www DOT peterflomconsulting DOT com
Writing; http://www.associatedcontent.com/user/582880/peter_flom.html
Twitter: @peterflom