car (version 3.0-10)

symbox: 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, ...)
# S3 method for formula
symbox(formula, data=NULL, subset, na.action=NULL, ylab,  ...)
# S3 method for default
symbox(x, powers = c(-1, -0.5, 0, 0.5, 1), start, 
	trans=bcPower, xlab="Powers", ylab, ...)



a numeric vector.


a one-sided formula specifying a single numeric variable.

data, subset, na.action

as for statistical modeling functions (see, e.g., lm).

xlab, ylab

axis labels; if ylab is missing, a label will be supplied.


a vector of selected powers to which x is to be raised. For meaningful comparison of powers, 1 should be included in the vector of powers.


a constant to be added to x. If start is missing and trans is bcPower (the default) or bcnPower, then a start will be automatically generated if there are zero or negative values in x, and a warning will be printed; the auto-generated start is the absolute value of the minimum x plus 1 percent of the range of x.


a transformation function whose first argument is a numeric vector and whose second argument is a transformation parameter, given by the powers argument; the default is bcPower, and another possibility is yjPower. bcnPower may also be used, in which case the gamma parameter is set to the value of start.

arguments to be passed down.


as returned by boxplot.


Fox, J. and Weisberg, S. (2019) An R Companion to Applied Regression, Third Edition. Sage.

See Also

boxplot, boxcox, bcPower, yjPower


symbox(~ income, data=Prestige)
# }