boxcox | R Documentation |

Computes and optionally plots profile log-likelihoods for the parameter of the Box-Cox power transformation.

```
boxcox(object, ...)
## Default S3 method:
boxcox(object, lambda = seq(-2, 2, 1/10), plotit = TRUE,
interp, eps = 1/50, xlab = expression(lambda),
ylab = "log-Likelihood", ...)
## S3 method for class 'formula'
boxcox(object, lambda = seq(-2, 2, 1/10), plotit = TRUE,
interp, eps = 1/50, xlab = expression(lambda),
ylab = "log-Likelihood", ...)
## S3 method for class 'lm'
boxcox(object, lambda = seq(-2, 2, 1/10), plotit = TRUE,
interp, eps = 1/50, xlab = expression(lambda),
ylab = "log-Likelihood", ...)
```

`object` |
a formula or fitted model object. Currently only |

`lambda` |
vector of values of |

`plotit` |
logical which controls whether the result should be plotted. |

`interp` |
logical which controls whether spline interpolation is
used. Default to |

`eps` |
Tolerance for |

`xlab` |
defaults to |

`ylab` |
defaults to |

`...` |
additional parameters to be used in the model fitting. |

A list of the `lambda`

vector and the computed profile
log-likelihood vector, invisibly if the result is plotted.

If `plotit = TRUE`

plots log-likelihood *vs* `lambda`

and
indicates a 95% confidence interval about the maximum observed value
of `lambda`

. If `interp = TRUE`

, spline interpolation is
used to give a smoother plot.

Box, G. E. P. and Cox, D. R. (1964)
An analysis of transformations (with discussion).
*Journal of the Royal Statistical Society B*, **26**, 211–252.

Venables, W. N. and Ripley, B. D. (2002)
*Modern Applied Statistics with S.* Fourth edition. Springer.

```
boxcox(Volume ~ log(Height) + log(Girth), data = trees,
lambda = seq(-0.25, 0.25, length.out = 10))
boxcox(Days+1 ~ Eth*Sex*Age*Lrn, data = quine,
lambda = seq(-0.05, 0.45, length.out = 20))
```

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