psych (version 1.0-97)

ellipses: Plot data and 1 and 2 sigma correlation ellipses

Description

For teaching correlation, it is useful to draw ellipses around the mean to reflect the correlation. This variation of the ellipse function from John Fox's car package does so. Input may be either two vectors or a matrix or data.frame. In the latter cases, if the number of variables >2, then the ellipses are done in the pairs.panels function. Ellipses may be added to existing plots. The minkowski function is included as a generalized ellipse.

Usage

ellipses(x, y = NULL, add = FALSE, smooth=TRUE, lm=FALSE,data=TRUE, n = 2,span=2/3, iter=3, col = "red", xlab =NULL,ylab= NULL, ...)
minkowski(r=2,add=FALSE,main=NULL,xl=1,yl=1)

Arguments

x
a vector,matrix, or data.frame
y
Optional second vector
add
Should a new plot be created, or should it be added to?
smooth
smooth = TRUE -> draw a loess fit
lm
lm=TRUE -> draw the linear fit
data
data=TRUE implies draw the data points
n
Should 1 or 2 ellipses be drawn
span
averaging window parameter for the lowess fit
iter
iteration parameter for lowess
col
color of ellipses (default is red
xlab
label for the x axis
ylab
label for the y axis
...
Other parameters for plotting
r
r=1 draws a city block, r=2 is a Euclidean circle, r > 2 tends towards a square
main
title to use when drawing Minkowski circles
xl
stretch the x axis
yl
stretch the y axis

Value

  • A single plot (for 2 vectors or data frames with fewer than 3 variables. Otherwise a call is made to pairs.panels.

Details

Ellipse dimensions are calculated from the correlation between the x and y variables and are scaled as sqrt(1+r) and sqrt(1-r).

References

Galton, Francis (1888), Co-relations and their measurement. Proceedings of the Royal Society. London Series, 45, 135-145.

See Also

pairs.panels

Examples

Run this code
data(galton)
ellipses(galton,lm=TRUE)
ellipses(galton$parent,galton$child,xlab="Mid Parent Height",ylab="Child Height") #input are two vectors
data(sat.act)
ellipses(sat.act)  #shows the pairs.panels ellipses
minkowski(2,main="Minkowski circles")
minkowski(1,TRUE)
minkowski(4,TRUE)

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