# bickeldoksum: Bickel-Doksum transformation for linear models In trafo: Estimation, Comparison and Selection of Transformations

## Description

The function transforms the dependent variable of a linear model using the Bickel-Doksum transformation. The transformation parameter can either be estimated using different estimation methods or given.

## Usage

 ```1 2``` ```bickeldoksum(object, lambda = "estim", method = "ml", lambdarange = c(1e-11, 2), plotit = TRUE) ```

## Arguments

 `object` an object of type lm. `lambda` either a character named "estim" if the optimal transformation parameter should be estimated or a numeric value determining a given value for the transformation parameter. Defaults to "estim". `method` a character string. Different estimation methods can be used for the estimation of the optimal transformation parameter: (i) Maximum likelihood approach ("ml"), (ii) Skewness minimization ("skew"), (iii) Kurtosis optimization ("kurt"), (iv) Divergence minimization by Kolmogorov-Smirnov ("div.ks"), by Cramer-von-Mises ("div.cvm") or by Kullback-Leibler ("div.kl"). Defaults to "ml". `lambdarange` a numeric vector with two elements defining an interval that is used for the estimation of the optimal transformation parameter. The Bickel-Doksum transformation is only defined for positive values of lambda. Defaults to `c(1e-11, 2)`. `plotit` logical. If `TRUE`, a plot that illustrates the optimal transformation parameter or the given transformation parameter is returned. Defaults to `TRUE`.

## Value

An object of class `trafo`. Methods such as `as.data.frame.trafo` and `print.trafo` can be used for this class.

## References

Bickel PJ, Doksum KA (1981). An analysis of transformations revisited. Journal of the American Statistical Association, 76, 296-311.

## Examples

 ```1 2 3 4 5 6 7 8``` ```# Load data data("cars", package = "datasets") # Fit linear model lm_cars <- lm(dist ~ speed, data = cars) # Transform dependent variable using a maximum likelihood approach bickeldoksum(object = lm_cars, plotit = FALSE) ```

trafo documentation built on May 2, 2019, 2:13 p.m.