# lmer

##### Fit (Generalized) Linear Mixed-Effects Models

Fit a linear or generalized linear mixed-effects model with nested or crossed grouping factors for the random effects.

##### Usage

```
lmer(formula, data, family, method, control, start,
subset, weights, na.action, offset, contrasts,
model, ...)
lmer2(formula, data, family, method, control, start,
subset, weights, na.action, offset, contrasts,
model, ...)
```

##### 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. The vertical bar character - data
- an optional data frame containing the variables named in
`formula`

. By default the variables are taken from the environment from which`lmer`

is called. - family
- a GLM family, see
`glm`

. If`family`

is missing then a linear mixed model is fit; otherwise a generalized linear mixed model is fit. - method
- a character string. For a linear mixed model the
default is
`"REML"`

indicating that the model should be fit by maximizing the restricted log-likelihood. The alternative is`"ML"`

indicating that the log-likelihood shou - control
- a list of control parameters. See below for details.
- start
- a list of relative precision matrices for the random
effects. This has the same form as the slot
`"Omega"`

in a fitted model. Only the upper triangle of these symmetric matrices should be stored. - subset, weights, na.action, offset, contrasts
- further model
specification arguments as in
`lm`

; see there for details. - model
- logical indicating if the model component
should be returned (in slot
`frame`

). - ...
- potentially further arguments for methods. Currently none are used.

##### Details

This is a revised version of the `lme`

function from the

The `lmer2`

function is a development version of `lmer`

that
uses a modified internal representation of the model. Typically
`lmer2`

is faster and more reliable than `lmer`

. At present
`lmer2`

can only fit linear mixed-effects models (that is, the
`family`

argument must be left unspecified) and not all the
methods for `"lmer"`

objects are defined for `"lmer2"`

objects. In particular, there is no `mcmcsamp`

method for
`"lmer2"`

objects.

When all the methods for the `"lmer"`

objects and all the options
for the `lmer`

function have been duplicated for the new
representation, the new representation will replace the old one and
the `"2"`

will be dropped from the name.
Additional standard arguments to model-fitting functions can be passed
to `lmer`

.
[object Object],[object Object],[object Object],[object Object]

##### Value

- An object of class
`"`

. There are many methods applicable tolmer "`"lmer"`

objects, see the above help page.

##### concept

GLMM

##### See Also

The

class, `lm`

##### Examples

```
(fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy))
(fm2 <- lmer(Reaction ~ Days + (1|Subject) + (0+Days|Subject), sleepstudy))
anova(fm1, fm2)
```

*Documentation reproduced from package lme4, version 0.99875-2, License: GPL version 2 or later*