testTransform: Likelihood-Ratio Tests for Univariate or Multivariate Power Transformations
to Normality
Description
testTransform computes likelihood ratio tests for particular transformations
based on powerTransform objects.
Usage
testTransform(object, lambda)
## S3 method for class 'powerTransform':
testTransform(object, lambda=rep(1, dim(object$y)[2]))
Arguments
object
An object created by a call to
estimateTransform or powerTransform.
lambda
A vector of values of length equal to the number of
variables to be transformed.
Value
A data frame with one row giving the value of the test statistic, its
degrees of freedom, and a p-value. The test is the likelihood ratio test,
comparing the value of the log-likelihood at the hypothesized value to
the value of the log-likelihood at the maximum likelihood estimate.
Details
The function powerTransform is used to estimate a power
transformation for a univariate or multivariate sample or multiple linear
regression problem, using the method of Box and Cox (1964). It is usual to
round the estimates to nearby convenient values, and this function is use to
compulte a likelihood ratio test for values of the transformation parameter
other than the ml estimate. This is a generic function, but with only one
method, for objects of class powerTransform.
References
Box, G. E. P. and Cox, D. R. (1964) An analysis of transformations. Journal
of the Royal Statisistical Society, Series B. 26 211-46.
Cook, R. D. and Weisberg, S. (1999) Applied Regression Including Computing
and Graphics. Wiley.
Fox, J. and Weisberg, S. (2011)
An R Companion to Applied Regression, Second Edition, Sage.
Weisberg, S. (2005) Applied Linear Regression, Third Edition. Wiley.