I believe that the following is the problem: For the regression of x on y, you have to move y to the left-hand-side of the equation to plot the line in {x, y}; so if the regression equation from the model x.y is x = a + b y, you need abline(-a/b, 1/b).
I hope that this helps, John
At 09:17 AM 2/20/2004 -0500, Michael Friendly wrote:
I'm trying to do a sunflowerplot of Galton's data, with both regression lines and data ellipses,
and I must be doing something wrong, because the lines do not intersect at \bar{x}, \bar{y}.
The problem is likely in the line for x.y, but I don't know how to specify that correctly.
The data is read in grouped form( galton), and then ungrouped (galton2):
galton <- read.table("~/sasuser/data/galton.txt", header=TRUE) # ungroup galton2<-galton[rep(1:nrow(galton), galton$frequency), 1:2]
attach(galton) sunflowerplot(child, parent, number=frequency, xlim=c(61,75), ylim=c(61,75), xlab="Child height", ylab="Mid Parent height")
# both attempts plot the same, wrong regression lines y.x <- lm(parent ~ child, weights=frequency) abline(y.x) x.y <- lm(child ~ parent, weights=frequency) abline(x.y, col="gray")
attach(galton2) y.x <- lm(parent ~ child) abline(y.x, lwd=2) x.y <- lm(child ~ parent) abline(x.y, col="gray", lwd=2)
library(car) data.ellipse(child, parent, plot.points=FALSE, levels=c(0.40, 0.68), lty=2)
The resulting figure may be seen at http://euclid.psych.yorku.ca/SCS/Gallery/Private/galton.jpg
-Michael
-- Michael Friendly Email: [EMAIL PROTECTED] Professor, Psychology Dept. York University Voice: 416 736-5115 x66249 Fax: 416 736-5814 4700 Keele Street http://www.math.yorku.ca/SCS/friendly.html Toronto, ONT M3J 1P3 CANADA
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----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: [EMAIL PROTECTED] phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox
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