qualityTools (version 1.49)

qqPlot: Quantile-Quantile Plots for various distributions

Description

qqPlot creates a QQ plot of the values in x including a line which passes through the first and third quartiles.

Usage

qqPlot(x, y, main, xlab, ylab, xlim, ylim, border = "red", start, ...)

Arguments

x

the sample for qqPlot

y

character string specifying the distribution of x. The function qqPlot will support the following character strings for y:

• beta
• cauchy
• chi-squared

main

an overall title for the plot: see title.

xlab

a title for the x axis: title.

ylab

a title for the y axis: title.

xlim

vector giving the range of the x-axis.

ylim

vector giving the range of the y-axis.

border

numerical value or single character string giving the color of interpolation line. By default border is set to red.

start

A named list giving the parameters to be fitted with initial values. Must be supplied for some distribution: (see Details).

...

further graphical parameters: (see par).

Value

• a list containing the x and y quantiles
• x
  sample quantiles
• y
  theoretical quantiles

Details

Distribution fitting is deligated to function fitdistr of the R-package MASS.

See Also

fitdistr in R-package MASS http://www.user.tu-berlin.de/kalicete/qualityTools/S4.html#SS1.SSS3

Examples

#set up the plotting window for 6 plots
par(mfrow = c(3,2))

#generate random data from weibull distribution
x = rweibull(20, 8, 2)

#Quantile-Quantile Plot for different distributions
qqPlot(x, "log-normal")
qqPlot(x, "normal")
qqPlot(x, "exponential", DB = TRUE)
qqPlot(x, "cauchy")
qqPlot(x, "weibull")
qqPlot(x, "logistic")