vcrpart (version 1.0-6)

olmm-methods: Methods for olmm objects

Description

Standard methods for computing on olmm objects.

Usage

# S3 method for olmm
anova(object, ...)
# S3 method for olmm
coef(object, which = c("all", "fe"), ...)
# S3 method for olmm
fixef(object, which = c("all", "ce", "ge"), ...)
# S3 method for olmm
model.matrix(object, which = c("fe", "fe-ce", "fe-ge",
             "re", "re-ce", "re-ge"), ...)
# S3 method for olmm
neglogLik2(object, ...)
# S3 method for olmm
ranef(object, norm = FALSE, ...)
# S3 method for olmm
ranefCov(object, ...) 
# S3 method for olmm
simulate(object, nsim = 1, seed = NULL,
         newdata = NULL, ranef = TRUE, ...)
# S3 method for olmm
terms(x, which = c("fe-ce", "fe-ge", "re-ce", "re-ge"), ...)
# S3 method for olmm
VarCorr(x, sigma = 1., ...)
# S3 method for olmm
weights(object, level = c("observation", "subject"), ...)

Value

The anova.olmm method returns an object of class

anova, see also anova.

The coef.olmm, coefficients.olmm,

fixef, fixef.glm and

fixef.olmm methods return named numeric

vectors. See also coef and

coefficients.

The deviance.olmm method returns a single numeric, see also deviance.

The formula.olmm method extracts the model formula, which is an object of class formula. See also

formula.

The getCall.olmm method extracts the call for fitting the model, which is an object of class call. See also

call.

The logLik.olmm method returns an object of class

logLik, which is a single numeric with a few attributes. See also logLik.

The neglogLik2 and neglogLik2.olmm

methods return a single numeric.

The model.frame.olmm and

model.matrix.olmm methods return the model frame and the model matrix of the olmm object. See also

model.frame and model.matrix.

The ranef and ranef.olmm methods return a matrix with the estimated random effects.

The ranefCov and ranefCov.olmm

methods return an object of class matrix. The

VarCorr and VarCorr.olmm methods return an object of class

VarCorr.olmm. print.VarCorr.olmm returns an object of class VarCorr.olmm.

The resid.olmm and residuals.olmm

methods return a numeric vector.

The simulate.olmm method returns a data.frame

including simulated responses based on the input model.

The terms.olmm method returns an object of class

terms. See also terms.

The update.olmm method will update and (by default) re-fit a model. It returns an object of class olmm. See also

update.

The vcov.olmm method extracts a matrix with the variances and covariances of the fixed effects of the model. See also vcov.

The weights.olmm method extracts a numeric

vector with the model weights. See also weights.

Arguments

object, x

an olmm object.

which

optional character string. For coef and fixef, it indicates whether "all" coefficients, the fixed effects "fe", the category-specific fixed effects "ce" (i.e. non-proportional odds) or the global fixed effects "ge" (i.e. proportional odds) should be extracted. For model.matrix it indicates whether the model matrix of the fixed- ("fe") or the random effects ("re") should be extracted.

level

character string. Whether the results should be on the observation level (level = "observation") or on the subject level (level = "subject").

norm

logical. Whether residuals should be divided by their standard deviation.

nsim

number of response vectors to simulate. Defaults to 1.

seed

an object specifying if and how the random number generator should be initialized. See simulate

newdata

a data frame with predictor variables.

ranef

either a logical or a matrix (see predict.olmm). Whether the simulated responses should be conditional on random effects. If TRUE, the newdata data frame must contain the subject identification variable. Further, if all subjects in newdata are in object, the simulation will be based on the estimated random effects as obtained with ranef. If any subject in newdata is not in object the random effects are simulated.

sigma

ignored but obligatory argument from original generic.

...

potential further arguments passed to methods.

Author

Reto Burgin

Details

anova implements log-likelihood ratio tests for model comparisons, based on the marginal likelihood. At the time being, at least two models must be assigned.

neglogLik2 returns the marginal maximum likelihood of the fitted model times minus 2.

ranefCov extracts the variance-covariance matrix of the random effects. Similarly, VarCorr extracts the estimated variances, standard deviations and correlations of the random effects.

resid extracts the residuals of Li and Sheperd (2012). By default, the marginal outcome distribution is used to compute these residuals. The conditional residuals can be computed by assigning ranef = TRUE as a supplementary argument.

simulate simulates ordinal responses based on the input model.

Further, undocumented methods are deviance, extractAIC, fitted, formula, getCall, logLik, model.frame, nobs, update, vcov.

The anova implementation is based on codes of the lme4 package. The authors are grateful for these codes.

References

Agresti, A. (2010). Analysis of Ordinal Categorical Data (2 ed.). New Jersey, USA: John Wiley & Sons.

Tutz, G. (2012). Regression for Categorical Data. New York, USA: Cambridge Series in Statistical and Probabilistic Mathematics.

Li, C. and B. E. Sheperd (2012). A New Residual for Ordinal Outcomes, Biometrika, 99(2), 437--480.

Bates, D., M. Maechler, B. M. Bolker and S. Walker (2015). Fitting Linear Mixed-Effects Models Using lme4, Journal of Statistical Software, 67(1), 1--48.

See Also

olmm, predict.olmm, olmm_gefp

Examples

## --------------------------------------------------------- #
## Example: Schizophrenia (see also example of 'olmm')
## --------------------------------------------------------- #

data(schizo)

schizo <- schizo[1:181,]
schizo$id <- droplevels(schizo$id)

## anova comparison
## ----------------

## fit two alternative models for the 'schizo' data
model.0 <- olmm(imps79o ~ tx + sqrt(week) + re(1|id), schizo)
model.1 <- olmm(imps79o ~ tx + sqrt(week)+tx*sqrt(week)+re(1|id),schizo)
anova(model.0, model.1)

## simulate responses
## ------------------

## simulate responses based on estimated random effects
simulate(model.0, newdata = schizo[1, ], ranef = TRUE, seed = 1)
simulate(model.0, newdata = schizo[1, ], seed = 1,
         ranef = ranef(model.0)[schizo[1, "id"],,drop=FALSE])
## simulate responses based on simulated random effects
newdata <- schizo[1, ]
newdata$id <- factor("123456789")
simulate(model.0, newdata = newdata, ranef = TRUE)

## other methods
## -------------

coef(model.1)
fixef(model.1)
head(model.matrix(model.1, "fe-ge"))
head(weights(model.1))
ranefCov(model.1)
head(resid(model.1))
terms(model.1, "fe-ge")
VarCorr(model.1)
head(weights(model.1, "subject"))