Plot for Box-Cox Transformation Analysis

DESCRIPTION:

Displays a log-likelihood plot and/or lambda plot using the results of a Box-Cox transformation analysis.

USAGE:

plot.boxcox(x, plot.type = "both", nlabs, conf = .95,...) 

REQUIRED ARGUMENTS:

x
object of class "boxcox", typically the output from performing a Box-Cox transformation analysis with boxcox.

OPTIONAL ARGUMENTS:

plot.type
character string giving type of plot: "lambda" asks for a plot of t-values for all terms in the reduced model over lambda values of Box-Cox tranformations, "loglik" asks for a plot of log-likelihoods over lambda values; "both" produces both types of plot.
nlabs
number of terms to be labelled in the lambda plot.
conf
confidence level at which to draw confidence limits on the lambda plot.
...
arguments to the function plot.

SIDE EFFECTS:

The plot or plots requested are drawn on the current graphics device.

DETAILS:

The log-likelihoods of different lambda values from a Box-Cox transformation analysis are plotted, showing which value of lambda maximizes the log-likelihood. A confidence interval for lambda is also plotted. The t-values for all terms in the reduced model associated with a Box-Cox transformation are plotted against lambda values. A two-sided confidence interval for significant effects is shown as well as the choice for the best lambda value.

REFERENCES:

Box, G.E.P. and D.R. Cox (1964) An analysis of transformations (with discussion). J. Royal Statist. Soc. Ser. B, 26:211-246

Box, G. E. P., W. G. Hunter, and J. S. Hunter (1978) Statistics for Experimenters, New York: Wiley.

Haaland, P. D. (1989) Experimental Design in Biotechnology, New York: Marcel Dekker.

SEE ALSO:

, , , .

EXAMPLES:

buffer.fac <- fac.aov(buffer.df) 
buffer.bc <- boxcox(buffer.fac, ~pH*thimer+pH*gent) 
plot(buffer.bc)