ci.plot {HH}R Documentation

Plot confidence and prediction intervals for simple linear regression

Description

The data, the least squares line, the confidence interval lines, and the prediction interval lines for a simple linear regression (lm(y ~ x)) are displayed. Tick marks are placed at the location of xbar, the x-value of the narrowest interval.

Usage

ci.plot(lm.object, ...)

## S3 method for class 'lm':
ci.plot(lm.object,
        xlim=range(data[, x.name]),
        newdata,
        conf.level=.95,
        data=model.frame(lm.object),
        newfit,
        ylim,
        pch=16,
        main.cex=1,
        main=list(paste(100*conf.level,
          "% confidence and prediction intervals for ",
          substitute(lm.object), sep=""), cex=main.cex), ...
        )

Arguments

lm.object Linear model for one y and one x variable.
xlim xlim for plot. Default is based on data from which lm.object was constructed.
newdata data.frame containing data for which predictions are wanted. The variable name of the column must be identical to the name of the predictor variable in the model object. Defaults to a data.frame containing a vector spanning the range of observed data. User-specified values are appended to the default vector.
conf.level Confidence level for intervals, defaults to .95
data data extracted from the lm.object
newfit Constructed data.frame containing the predictions,confidence interval, and prediction interval for the newdata.
ylim ylim for plot. Default is based on the constructed prediction interval.
pch Plotting character for observed points.
main.cex Font size for main title.
main Main title for plot
... Additional arguments to be passed to panel function.

Value

"trellis" object containing the plot.

Note

The predict.lm functions in S-Plus and R differ. The S-Plus function can produce both confidence and prediction intervals with a single call. The R function produces only one of them in a single call. Therefore the default calculation of newfit within the function depends on the system.

Author(s)

Richard M. Heiberger <rmh@temple.edu>

See Also

lm, predict.lm

Examples

tmp <- data.frame(x=rnorm(20), y=rnorm(20))
tmp.lm <- lm(y ~ x, data=tmp)
ci.plot(tmp.lm)

[Package HH version 2.1-25 Index]