boxcoxplot {s20x}R Documentation

Box-Cox Plot

Description

Draws a plot of the Box-Cox profile likelihood for the powers in the vector p. Used for selecting a power transformation for symmetrising a single batch (if the argument "group" is missing), or normalising the data (if the argument "group" is present). The most suitable p value is given by the minimum of the Box-Cox plot.

Usage

boxcoxplot(x, group, p = seq(-1, 2, length = 20),...)

Arguments

x a vector containing the data from which the boxcoxplots are to be produced.
group a vector containing the group labels.
p gives the set of values of p over which the plot should range. The default takes 20 equally-spaced values over the range p=-1 to p=2. Use a different range if, for example, the minimum of the Box-Cox plot isn't in the interval [-1,2].
... plotting arguments such as axis labels (xlab,ylab) and titles (main).

Value

Returns no value but draws the plot.

See Also

Studies indicate that the Box-Cox plot is the best for choosing the power, followed by the skewness power plot; "skewpowerplot": aims to eliminate skewness, "sympowerplot": aims for a symmetrising transformation.

Examples

##Income data:
data(incomes)
attach(incomes)
boxcoxplot(incomes)
detach(incomes)
##Sentence Length data: p120,156 1995 Data Analysis-an introduction based on R
sentence.lengths<-c(26,10,13,8,9,13,20,13,5,9,14,18,24,7,5,7,14,25,9,2,5,10,33,
7,11,10,10,17,5,8,10,16,12,23,11,13,8,17,10,31,9,27,5,6,12,21,7,41,9,5,19,3,9,
14,33,14,7,9,14,11,24,30,6,9,3,8,21,16,14,7,10,31,15,4,20,16,17,12,24,20)
book<-rep(c("IF","BDB","BG","CG"),c(20,20,20,20))
boxcoxplot(sentence.lengths,book)

[Package s20x version 2.0.1 Index]