vcov {ltm}R Documentation

vcov method for fitted IRT models

Description

Extracts the asymptotic variance-covariance matrix of the MLEs from either grm, ltm, rasch or tpm objects.

Usage


## S3 method for class 'grm':
vcov(object, ...)

## S3 method for class 'ltm':
vcov(object, robust = FALSE, ...)

## S3 method for class 'rasch':
vcov(object, robust = FALSE, ...)

## S3 method for class 'tpm':
vcov(object, ...)

Arguments

object an object inheriting from either class grm, class ltm, class rasch or class tpm.
robust logical; if TRUE the sandwich estimator is used.
... additional arguments; currently none is used.

Value

a numeric matrix representing the estimated covariance matrix of the maximum likelihood estimates.

Author(s)

Dimitris Rizopoulos dimitris.rizopoulos@med.kuleuven.be

See Also

grm, ltm, rasch, tpm

Examples


m <- grm(Science[c(1,3,4,7)], Hessian = TRUE)
vcov(m)

m <- rasch(Wirs)
vcov(m)
sqrt(diag(vcov(m))) # standard errors


[Package ltm version 0.6-0 Index]