car (version 1.2-10)

av.plots: Added-Variable Plots

Description

These functions construct added-variable (also called partial-regression) plots for linear and generalized linear models.

Usage

av.plots(model, variable, ask=missing(variable), one.page=!ask, ...)

avp(...)

av.plot(model, ...)

## S3 method for class 'lm':
av.plot(model, variable, 
  labels=names(residuals(model)[!is.na(residuals(model))]), 
  identify.points=TRUE, las=par("las"), col=palette()[2], pch=1, lwd=2,
  main="Added-Variable Plot", ...)

## S3 method for class 'glm':
av.plot(model, variable, 
    labels=names(residuals(model)[!is.na(residuals(model))]), 
    identify.points=TRUE, las=par("las"), col=palette()[2], pch=1, lwd=2, 
    main="Added-Variable Plot", type=c("Wang", "Weisberg"), ...)

Arguments

model

model object produced by lm or glm.

variable

variable (if it exists in the search path) or name of variable. This argument usually is omitted for avp or av.plots.

ask

if TRUE, a menu is provided in the R Console for the user to select the term(s) to plot.

one.page

if TRUE (and ask=FALSE), put all plots on one graph.

labels

observation names.

identify.points

if TRUE, then identify points interactively.

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).

main

title for plot.

type

if "Wang" use the method of Wang (1985); if "Weisberg" use the method in the Arc software associated with Cook and Weisberg (1999).

...

arguments to be passed down to av.plot.lm or av.plot.glm.

Value

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

Details

The function intended for direct use is av.plots (for which avp is an abbreviation). By default, these functions are used interactively through a text menu. The model can contain factors and interactions. An added-variable plot can be drawn for each column of the model matrix, including the constant.

References

Cook, R. D. and Weisberg, S. (1999) Applied Regression, Including Computing and Graphics. Wiley. Fox, J. (1997) Applied Regression, Linear Models, and Related Methods. Sage. Wang, P C. (1985) Adding a variable in generalized linear models. Technometrics 27, 273--276.

See Also

cr.plots, ceres.plots, leverage.plots

Examples

av.plots(lm(prestige~income+education+type, data=Duncan))

av.plots(glm(partic != "not.work" ~ hincome + children, 
  data=Womenlf, family=binomial))