`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.
For the `"lm"`

method, the response variable in the model is successively
transformed.

```
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, ...)
# S3 method for lm
symbox(x, powers = c(-1, -0.5, 0, 0.5, 1), start, trans=bcPower,
xlab, ylab="Studentized residuals", ...)
```

as returned by `boxplot`

.

- 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. For the`"lm"`

method, if`xlab`

is missing, a label will also 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.

Gregor Gorjanc, John Fox jfox@mcmaster.ca.

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

```
symbox(~ income, data=Prestige)
symbox(lm(wages ~ education + poly(age, 2) + sex, data=SLID))
```

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