boxTidwell {car} | R Documentation

## Box-Tidwell Transformations

### Description

Computes the Box-Tidwell power transformations of the predictors in a linear model.

### Usage

    boxTidwell(y, ...)

    ## S3 method for class 'formula'
    boxTidwell(formula, other.x=NULL, data=NULL, subset,
      na.action=getOption("na.action"), verbose=FALSE, tol=0.001,
      max.iter=25, ...)

    ## Default S3 method:
    boxTidwell(y, x1, x2=NULL, max.iter=25, tol=0.001,
      verbose=FALSE, ...)

    ## S3 method for class 'boxTidwell'
    print(x, digits, ...)

### Arguments

`formula` | two-sided formula, the right-hand-side of which gives the predictors to be transformed.
`other.x` | one-sided formula giving the predictors that are not candidates for transformation, including (e.g.) factors.
`data` | an optional data frame containing the variables in the model. By default the variables are taken from the environment from which `boxTidwell` is called.
`subset` | an optional vector specifying a subset of observations to be used.
`na.action` | a function that indicates what should happen when the data contain `NA`s. The default is set by the `na.action` setting of `options`.
`verbose` | if `TRUE` a record of iterations is printed; default is `FALSE`.
`tol` | if the maximum relative change in coefficients is less than `tol` then convergence is declared.
`max.iter` | maximum number of iterations.
`y` | response variable.
`x1` | matrix of predictors to transform.
`x2` | matrix of predictors that are not candidates for transformation.
`...` | not for the user.
`x` | `boxTidwell` object.
`digits` | number of digits for rounding.

### Details

The maximum-likelihood estimates of the transformation parameters are computed by Box and Tidwell's (1962) method, which is usually more efficient than using a general nonlinear least-squares routine for this problem. Score tests for the transformations are also reported.

### Value

an object of class `boxTidwell`, which is normally just printed.

### Author(s)

John Fox jfox@mcmaster.ca

### References

Box, G. E. P. and Tidwell, P. W. (1962) Transformation of the independent variables. Technometrics 4, 531-550.

Fox, J. (2008) Applied Regression Analysis and Generalized Linear Models, Second Edition. Sage.

Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.

### Examples

    boxTidwell(prestige ~ income + education, ~ type + poly(women, 2), data=Prestige)

[Package car version 2.1-6 Index]