cg (version 1.0-3)

fit.cgPairedDifferenceData: Fit models to a cgPairedDifferenceData object

Description

Fits a paired difference model based on the cgPairedDifferenceData object. The created object is designed for paired samples collected data, and is of class cgPairedDifferenceFit.

Usage

"fit"(data, type="rr", ...)

Arguments

data

A data object of class cgPairedDifferenceData.

type

Type of model to fit, represented by a character value. The default value is "rr". The two current possibilities are:

"ols"

Only fit an ordinary, classical least squares model with the base lm linear model function.

"rr"

Fit a Resistant / Robust model based on M- and S-estimation, using the rlm function from the MASS package (Venables and Ripley, 2002). This is the default character value for the type argument. See the ... argument and Details below for what options are available when rlm is used in this wrapper method.

...

Additional arguments, both optional, that are allowed to be specified dependent on the choice of the type argument. Otherwise they have no effect on the fit:

maxIter

If type="rr" then maxIter can be specified as a numeric postive integer. The default value of maxIter is 100. This gets passed to the maxit argument in the rlm method.

Value

Creates an object of class cgPairedDifferenceFit, with the following slots:

olsfit

The contents of a lm fit to the data. This is always populated with an lm object no matter the choice of the type argument, such as code="rr".

rrfit

The contents of a rlm fit to the data, housed as a rrfit class object. If type="rr" is not selected, then this is set to a simple character value of "No fit was selected.".

settings

A list of properties carried as-is from the data argument object of class cgPairedDifferenceData. In particular, if zeroscore is specified as a non-NULL number in the cgPairedDifferenceData object in the data argument, then a score value near zero was derived to replace all zeroes for subsequent log-scale analyses. Alternatively, if addconstant is specified as a non-NULL number in the cgPairedDifferenceData object in the data argument, then a value was added to shift up all observations for subsequent log-scale analyses.

Details

In the current version of the cg package, most default settings for rlm are kept for the fit.cgPairedDifferenceData method wrapper call when type="rr", with no capability to choose another value for an arguments such as psi, scale.est, and k2. The method argument is set to "MM".

References

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

Examples

data(anorexiaFT)
anorexiaFT.data <- prepareCGPairedDifferenceData(anorexiaFT, format="groupcolumns",
                                                 analysisname="Anorexia FT",
                                                 endptname="Weight",
                                                 endptunits="lbs",
                                                 expunitname="Patient",
                                                 digits=1, logscale=TRUE)
anorexiaFT.fit <- fit(data=anorexiaFT.data, type="rr")