transformTukey: Tukey's Ladder of Powers

In rcompanion: Functions to Support Extension Education Program Evaluation

Tukey's Ladder of Powers

Description

Conducts Tukey's Ladder of Powers on a vector of values to produce a more-normally distributed vector of values.

Usage

transformTukey(
  x,
  start = -10,
  end = 10,
  int = 0.025,
  plotit = TRUE,
  verbose = FALSE,
  quiet = FALSE,
  statistic = 1,
  returnLambda = FALSE
)

Arguments

x	A vector of values.
start	The starting value of lambda to try.
end	The ending value of lambda to try.
int	The interval between lambda values to try.
plotit	If TRUE, produces plots of Shapiro-Wilks W or Anderson-Darling A vs. lambda, a histogram of transformed values, and a quantile-quantile plot of transformed values.
verbose	If TRUE, prints extra output for Shapiro-Wilks W or Anderson-Darling A vs. lambda.
quiet	If TRUE, doesn't print any output to the screen.
statistic	If 1, uses Shapiro-Wilks test. If 2, uses Anderson-Darling test.
returnLambda	If TRUE, returns only the lambda value, not the vector of transformed values.

Details

The function simply loops through lamdba values from start to end at an interval of int.

The function then chooses the lambda which maximizes the Shapiro-Wilks W statistic or minimizes the Anderson-Darling A statistic.

It may be beneficial to add a constant to the input vector so that all values are posititive. For left-skewed data, a (Constant - X) transformation may be helpful. Large values may need to be scaled.

Value

The transformed vector of values. The chosen lambda value is printed directly.

Author(s)

Salvatore Mangiafico, [e-mail]

References

https://rcompanion.org/handbook/I_12.html

Examples

### Log-normal distribution example
Conc = rlnorm(100)
Conc.trans = transformTukey(Conc)
                      

rcompanion documentation built on Sept. 17, 2023, 5:07 p.m.