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, statistic = 1)
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.
statistic
If 1, uses Shapiro-Wilks test.
If 2, uses Anderson-Darling test.
Value
The transformed vector of values. The chosen lambda value is printed
directly.
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.