makeTube: Regression tube

In JECheadle/RSOC317L: Data Sets and Supplemental Functions from David Diez's 'OpenIntro' Textbook

Description

Produce a linear, quadratic, or nonparametric tube for regression data.

Usage

makeTube(x, y, Z=2, R=1, col='#00000022', border='#00000000',
  type=c('lin', 'quad', 'robust'), stDev=c('constant', 'linear', 'other'),
  length.out=99, bw='default', plotTube=TRUE, addLine=TRUE, ...)

Arguments

x	x coordinates.
y	y coordinates.
Z	Number of standard deviations out from the regression line to extend the tube.
R	Control of how far the tube extends to the left and right.
col	Fill color of the tube.
border	Border color of the tube.
type	The type of model fit to the data. Here 'robust' results in a nonparametric estimate.
stDev	Choices are constant variance ('constant'), the standard deviation of the errors changes linearly ('linear'), or the standard deviation of the errors should be estimated using nonparametric methods ('other').
length.out	The number of observations used to build the regression model. This argument may be increased to increase the smoothing of a quadratic or nonparametric curve.
bw	Bandwidth used if type='robust' or homosk=FALSE.
plotTube	Whether the tube should be plotted.
addLine	Whether the linear model should be plotted.
...	Additional arguments passed to the lines function if addLine=TRUE.

Value

X	x coordinates for the regression model.
Y	y coordinates for the regression model.
tubeX	x coordinates for the boundary of the tube.
tubeY	y coordinates for the boundary of the tube.

Author(s)

David M Diez

See Also

lmPlot

Examples

#===> possum example <===#
data(possum)
x <- possum$totalL
y <- possum$headL
plot(x,y)
makeTube(x,y,1)
makeTube(x,y,2)
makeTube(x,y,3)

#===> Grades and TV example <===#
data(gradesTV)
par(mfrow=c(2,2))
plot(gradesTV)
makeTube(gradesTV$TV, gradesTV$Grades, 1.5)
plot(gradesTV)
makeTube(gradesTV$TV, gradesTV$Grades, 1.5, stDev='o')
plot(gradesTV)
makeTube(gradesTV$TV, gradesTV$Grades, 1.5, type='robust')
plot(gradesTV)
makeTube(gradesTV$TV, gradesTV$Grades, 1.5, type='robust', stDev='o')

#===> What can go wrong with a basic least squares model <===#
par(mfrow=c(1,3), mar=c(2.5, 2.5, 1, 2.5))
# 1
x <- runif(100)
y <- 25*x-20*x^2+rnorm(length(x), sd=1.5)
plot(x,y)
makeTube(x,y,type='q')
# 2
x <- c(-0.6, -0.46, -0.091, runif(97))
y <- 25*x + rnorm(length(x))
y[2] <- y[2] + 8
y[1] <- y[1] + 1
plot(x,y,ylim=range(y)+c(-10,5))
makeTube(x,y)
# 3
x <- runif(100)
y <- 5*x + rnorm(length(x), sd=x)
plot(x,y)
makeTube(x, y, stDev='l', bw=0.03)

JECheadle/RSOC317L documentation built on May 15, 2019, 4:02 a.m.