Ellipses {car}R Documentation

Ellipses, Data Ellipses, and Confidence Ellipses

Description

These functions draw ellipses, including data ellipses, and confidence ellipses for linear and generalized linear models.

Usage

ellipse(center, shape, radius, log="", center.pch=19, center.cex=1.5, 
  segments=51, add=TRUE, xlab="", ylab="", 
   col=palette()[2], lwd=2, fill=FALSE, fill.alpha=0.3, grid=TRUE, ...)

dataEllipse(x, y, log="", levels=c(0.5, 0.95), center.pch=19, center.cex=1.5, 
  plot.points=TRUE, add=!plot.points, segments=51, robust=FALSE,
  xlab=deparse(substitute(x)), 
  ylab=deparse(substitute(y)), 
  col=palette()[1:2], lwd=2, fill=FALSE, fill.alpha=0.3, grid=TRUE, ...)

confidenceEllipse(model, ...)

## S3 method for class 'lm'
confidenceEllipse(model, which.coef, levels=0.95, Scheffe=FALSE, 
  center.pch=19, center.cex=1.5, segments=51, xlab, ylab, 
  col=palette()[2], lwd=2, fill=FALSE, fill.alpha=0.3, add=FALSE, ...)

## S3 method for class 'glm'
confidenceEllipse(model, which.coef, levels=0.95, Scheffe=FALSE, 
  center.pch=19, center.cex=1.5, segments=51, xlab, ylab, 
  col=palette()[2], lwd=2, fill=FALSE, fill.alpha=0.3, add=FALSE, ...)

Arguments

center 2-element vector with coordinates of center of ellipse.
shape 2 * 2 shape (or covariance) matrix.
radius radius of circle generating the ellipse.
log when an ellipse is to be added to an existing plot, indicates whether computations were on logged values and to be plotted on logged axes; "x" if the x-axis is logged, "y" if the y-axis is logged, and "xy" or "yx" if both axes are logged. The default is "", indicating that neither axis is logged.
center.pch character for plotting ellipse center.
center.cex relative size of character for plotting ellipse center.
segments number of line-segments used to draw ellipse.
add if TRUE add ellipse to current plot.
xlab label for horizontal axis.
ylab label for vertical axis.
x a numeric vector, or (if y is missing) a 2-column numeric matrix.
y a numeric vector, of the same length as x.
plot.points if FALSE data ellipses are added to the current scatterplot, but points are not plotted.
levels draw elliptical contours at these (normal) probability or confidence levels.
robust if TRUE use the cov.trob function in the MASS package to calculate the center and covariance matrix for the data ellipse.
model a model object produced by lm or glm.
which.coef 2-element vector giving indices of coefficients to plot; if missing, the first two coefficients (disregarding the regression constant) will be selected.
Scheffe if TRUE scale the ellipse so that its projections onto the axes give Scheffe confidence intervals for the coefficients.
col color for lines and ellipse center; the default is the second entry in the current color palette (see palette and par). For dataEllipse, two colors can be given, in which case the first is for plotted points and the second for lines and the ellipse center.
lwd line width; default is 2 (see par).
fill fill the ellipse with translucent color col (default, FALSE)?
fill.alpha transparency of fill (default = 0.3).
... other plotting parameters to be passed to plot and line.
grid If TRUE, the default, a light-gray background grid is put on the graph

Details

The ellipse is computed by suitably transforming a unit circle.

dataEllipse superimposes the normal-probability contours over a scatterplot of the data.

Value

NULL. These functions are used for their side effect: producing plots.

Author(s)

Georges Monette Georges.Monette@mathstat.YorkU.CA and John Fox jfox@mcmaster.ca

References

Fox, J. (2008) Applied Regression Analysis and Generalized Linear Models, Second Edition. Sage.

Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.

Monette, G. (1990) Geometry of multiple regression and 3D graphics. In Fox, J. and Long, J. S. (Eds.) Modern Methods of Data Analysis. Sage.

See Also

cov.trob.

Examples

dataEllipse(Prestige$income, Prestige$education, levels=0.1*1:9, lty=2, 
	fill=TRUE, fill.alpha=0.1)
confidenceEllipse(lm(prestige~income+education, data=Prestige), Scheffe=TRUE)

[Package car version 2.0-9 Index]