logtrans {MASS}  R Documentation 
Find and optionally plot the marginal (profile) likelihood for alpha
for a transformation model of the form log(y + alpha) ~ x1 + x2 + ...
.
logtrans(object, ...) ## Default S3 method: logtrans(object, ..., alpha = seq(0.5, 6, by = 0.25)  min(y), plotit = TRUE, interp =, xlab = "alpha", ylab = "log Likelihood") ## S3 method for class 'formula': logtrans(object, data, ...) ## S3 method for class 'lm': logtrans(object, ...)
object 
Fitted linear model object, or formula defining the untransformed
model that is y ~ x1 + x2 + ... . The function is generic.

... 
If object is a formula, this argument may specify a data frame
as for lm .

alpha 
Set of values for the transformation parameter, alpha. 
plotit 
Should plotting be done? 
interp 
Should the marginal loglikelihood be interpolated with a spline
approximation? (Default is TRUE if plotting is to be done and
the number of real points is less than 100.)

xlab 
as for plot .

ylab 
as for plot .

data 
optional data argument for lm fit.

List with components x
(for alpha) and y
(for the marginal
loglikelihood values).
A plot of the marginal loglikelihood is produced, if requested, together with an approximate mle and 95% confidence interval.
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth edition. Springer.
logtrans(Days ~ Age*Sex*Eth*Lrn, data = quine, alpha = seq(0.75, 6.5, len=20))