lme {lme4}R Documentation

Fit linear mixed-effects models

Description

This generic function fits a linear mixed-effects model in the formulation described in Laird and Ware (1982) but allowing for nested random effects. The within-group errors are allowed to be correlated and/or have unequal variances.

Usage

lme(formula, data, random, ...)

Arguments

formula a two-sided linear formula object describing the fixed-effects part of the model, with the response on the left of a ~ operator and the terms, separated by + operators, on the right.
data an optional data frame containing the variables named in formula, random, correlation, weights, and subset. By default the variables are taken from the environment from which lme is called.
random optionally, 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 factor; or (iii) a named list of formulas.
... Optional arguments for methods. Currently none are used.

Details

Additional standard arguments to model-fitting functions can be passed to lme.

correlation
an optional corStruct object describing the within-group correlation structure. See the documentation of corClasses for a description of the available corStruct classes. Defaults to NULL, corresponding to no within-group correlations.
weights
an optional varFunc object or one-sided formula describing the within-group heteroscedasticity structure. If given as a formula, it is used as the argument to varFixed, corresponding to fixed variance weights. See the documentation on varClasses for a description of the available varFunc classes. Defaults to NULL, corresponding to homocesdatic within-group errors.
subset
an optional expression indicating the subset of the rows of data that should be used in the fit. This can be a logical vector, or a numeric vector indicating which observation numbers are to be included, or a character vector of the row names to be included. All observations are included by default.
method
a character string. If "REML" the model is fit by maximizing the restricted log-likelihood. If "ML" the log-likelihood is maximized. Defaults to "REML".
na.action
a function that indicates what should happen when the data contain NAs. The default action (na.fail) causes lme to print an error message and terminate if there are any incomplete observations.
control
a list of control values for the estimation algorithm to replace the default values returned by the function lmeControl. Defaults to an empty list.
model, x
logicals. If TRUE the corresponding components of the fit (the model frame, the model matrices) are returned.

Value

An lme-class{lme} object.

See Also

lme-class, lm

Examples

data(bdf)
fm <- lme(langPOST ~ IQ.ver.cen + avg.IQ.ver.cen, data = bdf,
          random = ~ IQ.ver.cen | schoolNR)
summary(fm)
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