Random Effects Structure

DESCRIPTION:

This function is a constructor for the reStruct class, representing a random effects structure and consisting of a list of pdMat objects, plus a settings attribute containing information for the optimization algorithm used to fit the associated mixed-effects model.

USAGE:

reStruct(object, pdClass, REML, data) 

REQUIRED ARGUMENTS:

object
any of the following: (i) a one-sided formula of the form ~x1+...+xn | g1/.../gm, with x1+...+xn specifying the model for the random effects and g1/.../gm the grouping structure ( m may be equal to 1, in which case no / is required). The random effects formula will be repeated for all levels of grouping, in the case of multiple levels of grouping; (ii) a list of one-sided formulas of the form `~x1+...+xn | g', with possibly different random effects models for each grouping level. The order of nesting will be assumed the same as the order of the elements in the list; (iii) a one-sided formula of the form `~x1+...+xn', or a pdMat object with a formula (i.e. a non- NULL value for formula(object)), or a list of such formulas or pdMat objects. In this case, the grouping structure formula will be derived from the data used to fit the mixed-effects model, which should inherit from class groupedData; (iv) a named list of formulas or pdMat objects as in (iii), with the grouping factors as names. The order of nesting will be assumed the same as the order of the order of the elements in the list; (v) an reStruct object.

OPTIONAL ARGUMENTS:

pdClass
an optional character string with the name of the pdMat class to be used for the formulas in object. Defaults to "pdSymm" which corresponds to a general positive-definite matrix.
REML
an optional logical value. If TRUE, the associated mixed-effects model will be fitted using restricted maximum likelihood; else, if FALSE, maximum likelihood will be used. Defaults to FALSE.
data
an optional data frame in which to evaluate the variables used in the random effects formulas in object. It is used to obtain the levels for factors, which affect the dimensions and the row/column names of the underlying pdMat objects. If NULL, no attempt is made to obtain information on factors appearing in the formulas. Defaults to the parent frame from which the function was called.

VALUE:

an object inheriting from class reStruct, representing a random effects structure.

SEE ALSO:

, ,

EXAMPLES:

rs1 <- reStruct(list(Dog = ~day, Side = ~1), data = Pixel) 
rs1 

fm1 <- lme(distance ~ age, data=Orthodont) # random is ~ age
fm1$modelStruct$reStruct