car (version 3.0-10)

# symbox: Boxplots for transformations to symmetry

## Description

`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.

## Usage

```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, ...)```

## Arguments

x

a numeric vector.

formula

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.

powers

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.

start

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`.

trans

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.

## Value

as returned by `boxplot`.

## References

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

## See Also

`boxplot`, `boxcox`, `bcPower`, `yjPower`

## Examples

```# NOT RUN {
symbox(~ income, data=Prestige)
# }
```