car (version 2.0-21)

leveragePlots: Regression Leverage Plots

Description

These functions display a generalization, due to Sall (1990) and Cook and Weisberg (1991), of added-variable plots to multiple-df terms in a linear model. When a term has just 1 df, the leverage plot is a rescaled version of the usual added-variable (partial-regression) plot.

Usage

leveragePlots(model, terms = ~., layout = NULL, ask, 
    main, ...)

leveragePlot(model, ...)

## S3 method for class 'lm':
leveragePlot(model, term.name,
    id.method = list(abs(residuals(model, type="pearson")), "x"),
    labels, 
    id.n = if(id.method[1]=="identify") Inf else 0,
    id.cex=1, id.col=palette()[1], 
    col=palette()[1], col.lines=palette()[2], lwd=2, 
    xlab, ylab, main="Leverage Plot", grid=TRUE, ...)

## S3 method for class 'glm':
leveragePlot(model, ...)

Arguments

model

model object produced by lm

terms

A one-sided formula that specifies a subset of the predictors. One added-variable plot is drawn for each term. The default ~. is to plot against all numeric predictors. For example, the specification terms = ~ . - X3 would

layout

If set to a value like c(1, 1) or c(4, 3), the layout of the graph will have this many rows and columns. If not set, the program will select an appropriate layout. If the number of graphs exceed nine, you must select the la

ask

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

xlab, ylab

axis labels; if missing, labels will be supplied.

main

title for plot; if missing, a title will be supplied.

...

arguments passed down to method functions.

term.name

Quoted name of term in the model to be plotted; this argument is omitted for leveragePlots.

id.method,labels,id.n,id.cex,id.col

Arguments for the labelling of points. The default is id.n=0 for labeling no points. See showLabels for details of these arguments.

col

color(s) of points

col.lines

color of the fitted line

lwd

line width; default is 2 (see par).

grid

If TRUE, the default, a light-gray background grid is put on the graph

Value

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

Details

The function intended for direct use is leveragePlots. The model can contain factors and interactions. A leverage plot can be drawn for each term in the model, including the constant. leveragePlot.glm is a dummy function, which generates an error message.

References

Cook, R. D. and Weisberg, S. (1991). Added Variable Plots in Linear Regression. In Stahel, W. and Weisberg, S. (eds.), Directions in Robust Statistics and Diagnostics. Springer, 47-60. 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. Sall, J. (1990) Leverage plots for general linear hypotheses. American Statistician 44, 308--315.

See Also

avPlots

Examples

leveragePlots(lm(prestige~(income+education)*type, data=Duncan))