boxcox {MASS} | R Documentation |
Computes and optionally plots profile log-likelihoods for the
parameter of the Box-Cox simple power transformation y^lambda
.
boxcox(object, lambda, plotit, interp, eps, xlab, ylab, ...)
object |
a formula or fitted model object. Currently only lm and aov objects
are handled.
|
lambda |
vector of values of lambda default (-2, 2) in steps of 0.1
|
plotit |
logical which controls whether the result should be plotted.
Default to true if a graphics device is currently open.
|
interp |
logical which controls whether spline interpolation is used.
Default to true if plotting with lambda of length less than 100.
|
eps |
Tolerance for lambda = 0 ; defaults to 0.02
|
xlab |
defaults to "lambda"
|
ylab |
defaults to "log-Likelihood"
|
... |
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 loglik 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.
data(trees) boxcox(Volume ~ log(Height) + log(Girth), data = trees, lambda = seq(-0.25, 0.25, length = 10)) boxcox(Days+1 ~ Eth*Sex*Age*Lrn, data = quine, lambda = seq(-0.05, 0.45, len = 20))