Boxplots for transformations to symmetry
symbox first transforms
x to each of a series
of selected powers, with each transformation standardized to mean 0 and
standard deviation 1. The results are then displayed side-by-side in boxplots, permiting
a visual assessment of which power makes the distribution reasonably symmetric.
symbox(x, powers=c(-1, -.5, 0, .5, 1), start=0)
- a numeric vector.
- a vector of selected powers to which
xis to be raised. A power of 0 is taken to mean $log(x)$. Negative powers are taken to mean $-x^p$, to preserve the order of the data. For meaningful comparison of powers, 1 s
- a constant to be added to
x; after adding the start, all data values must be positive.
- as returned by
Friendly, M. (2005) SAS System for Statistical Graphics, 2nd Edition. SAS Institute (In preparation).