ellipses {psych}

R Documentation

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,size=c(1,2), ...)
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
size	The size of ellipses in sd units (defaults to 1 and 2)
...	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

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). They are then scaled as size[1] and size[2] standard deviation units. To scale for 95 and 99 percent confidence use c(1.64,2.32)

Value

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

Note

Adapted from John Fox's ellipse and data.ellipse functions.

Author(s)

William Revelle

References

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

See Also

pairs.panels

Examples

data(psychTools::galton)
galton <- psychTools::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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