Ellipses

0th

Percentile

Ellipses, Data Ellipses, and Confidence Ellipses

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

Keywords
hplot, aplot
Usage
ellipse(center, shape, radius, center.pch=19, center.cex=1.5, 
  segments=51, add=TRUE, xlab="", ylab="", 
   las=par('las'), col=palette()[2], lwd=2, lty=1, ...)

data.ellipse(x, y, levels=c(0.5, 0.9), 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)), 
  las=par('las'), col=palette()[2], pch=1, lwd=2, lty=1, ...)

confidence.ellipse(model, ...)

## S3 method for class 'lm':
confidence.ellipse(model, which.coef, levels=0.95, Scheffe=FALSE, 
  center.pch=19, center.cex=1.5, segments=51, xlab, ylab, 
  las=par('las'), col=palette()[2], lwd=2, lty=1, ...)

## S3 method for class 'glm':
confidence.ellipse(model, which.coef, levels=0.95, Scheffe=FALSE, 
  center.pch=19, center.cex=1.5, segments=51, xlab, ylab, 
  las=par('las'), col=palette()[2], lwd=2, lty=1, ...)
Arguments
center
2-element vector with coordinates of center of ellipse.
shape
$2\times 2$ shape (or covariance) matrix.
radius
radius of circle generating the ellipse.
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.
las
if 0, ticks labels are drawn parallel to the axis; set to 1 for horizontal labels (see par).
col
color for points and lines; the default is the second entry in the current color palette (see palette and par).
pch
plotting character for points; default is 1 (a circle, see par).
lwd
line width; default is 2 (see par).
lty
line type; default is 1, a solid line (see par).
...
other plotting parameters to be passed to plot and line.
Details

The ellipse is computed by suitably transforming a unit circle. data.ellipse superimposes the normal-probability contours over a scatterplot of the data.

Value

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

References

Fox, J. (1997) Applied Regression, Linear Models, and Related Methods. 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.

Aliases
  • ellipse
  • data.ellipse
  • confidence.ellipse
  • confidence.ellipse.lm
  • confidence.ellipse.glm
Examples
data.ellipse(Prestige$income, Prestige$education, levels=0.1*1:9, lty=2)
confidence.ellipse(lm(prestige~income+education, data=Prestige), Scheffe=TRUE)
Documentation reproduced from package car, version 1.2-16, License: GPL (>= 2)

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