simulate.merMod {lme4} | R Documentation |
merMod
ObjectSimulate responses from a "merMod"
fitted model object, i.e.,
from the model represented by it.
## S3 method for class 'merMod' simulate(object, nsim = 1, seed = NULL, use.u = FALSE, re.form = NA, ReForm, REForm, REform, newdata=NULL, newparams=NULL, family=NULL, allow.new.levels = FALSE, na.action = na.pass, ...) ## S3 method for class 'formula' simulate(object, nsim = 1 , seed = NULL, family, weights=NULL, offset=NULL, ...) .simulateFun(object, nsim = 1, seed = NULL, use.u = FALSE, re.form = NA, ReForm, REForm, REform, newdata=NULL, newparams=NULL, formula=NULL, family=NULL, weights=NULL, offset=NULL, allow.new.levels = FALSE, na.action = na.pass, ...)
object |
(for |
nsim |
positive integer scalar - the number of responses to simulate. |
seed |
an optional seed to be used in |
use.u |
(logical) if |
re.form |
formula for random effects to condition on. If
|
ReForm, REForm, REform |
deprecated: |
newdata |
data frame for which to evaluate predictions. |
newparams |
new parameters to use in evaluating predictions,
specified as in the |
formula |
a (one-sided) mixed model formula, as described for
|
family |
a GLM family, as in |
weights |
|
offset |
offset, as in |
allow.new.levels |
(logical) if FALSE (default), then any new
levels (or |
na.action |
what to do with |
... |
optional additional arguments: none are used at present. |
ordinarily simulate
is used to generate new
values from an existing, fitted model (merMod
object):
however, if formula
, newdata
, and newparams
are
specified, simulate
generates the appropriate model
structure to simulate from.
The re.form
argument allows the user to specify how the
random effects are incorporated in the simulation. All of the
random effects terms included in re.form
will be
conditioned on - that is, the conditional modes of those
random effects will be included in the deterministic part of the
simulation. (If new levels are used (and allow.new.levels
is TRUE
), the conditional modes for these levels will be
set to the population mode, i.e. values of zero will be used for
the random effects.) Conversely, the random effect terms that are
not included in re.form
will be simulated
from - that is, new values will be chosen for each group based on
the estimated random-effects variances.
The default behaviour (using re.form=NA
) is to condition on
none of the random effects, simulating new values for all of the
random effects.
For Gaussian fits, sigma
specifies the residual
standard deviation; for Gamma fits, it specifies the shape
parameter (the rate parameter for each observation i
is calculated as shape/mean(i)). For negative binomial fits,
the overdispersion parameter is specified via the family,
e.g. simulate(..., family=negative.binomial(theta=1.5))
.
bootMer
for “simulestimate”, i.e., where each
simulation is followed by refitting the model.
## test whether fitted models are consistent with the ## observed number of zeros in CBPP data set: gm1 <- glmer(cbind(incidence, size - incidence) ~ period + (1 | herd), data = cbpp, family = binomial) gg <- simulate(gm1,1000) zeros <- sapply(gg,function(x) sum(x[,"incidence"]==0)) plot(table(zeros)) abline(v=sum(cbpp$incidence==0),col=2) ## ## simulate from a non-fitted model; in this case we are just ## replicating the previous model, but params <- list(theta=0.5,beta=c(2,-1,-2,-3)) simdat <- with(cbpp,expand.grid(herd=levels(herd),period=factor(1:4))) simdat$size <- 15 simdat$incidence <- sample(0:1,size=nrow(simdat),replace=TRUE) form <- formula(gm1)[-2] simulate(form,newdata=simdat,family=binomial, newparams=params)