discrpar {psychotools} | R Documentation |
A class and generic function for representing and extracting the discrimination parameters of a given item response model.
discrpar(object, ...) ## S3 method for class 'raschmodel' discrpar(object, ref = NULL, alias = TRUE, vcov = TRUE, ...) ## S3 method for class 'rsmodel' discrpar(object, ref = NULL, alias = TRUE, vcov = TRUE, ...) ## S3 method for class 'pcmodel' discrpar(object, ref = NULL, alias = TRUE, vcov = TRUE, ...)
object |
a fitted model object whose discrimination parameters should be extracted. |
ref |
a restriction to be used to ensure parameter
identifiability of the item discrimination parameters. Currently not
used as the item discrimination parameters are fixed to unity in
|
alias |
logical. If |
vcov |
logical. If |
... |
further arguments which are currently not used. |
discrpar
is both, a class to represent discrimination parameters
of item response models as well as a generic function. The generic
function can be used to extract the discrimination parameters of a
given item response model.
For objects of class discrpar
, several methods to standard
generic functions exist: print
, coef
, vcov
.
coef
and vcov
can be used to extract the discrimination
parameters and their variance-covariance matrix without additional
attributes.
A named vector with discrimination parameters of class
discrpar
and additional attributes model
(the model
name), ref
(the items or parameters used as restriction/for
normalization), alias
(either TRUE
or a named numeric
vector with the aliased parameters not included in the return value),
and vcov
(the estimated and adjusted variance-covariance matrix).
## load verbal aggression data data("VerbalAggression", package = "psychotools") ## fit a rasch model to dichotomized verbal aggression data rmod <- raschmodel(VerbalAggression$resp2) ## extract the discrimination parameters dp <- discrpar(rmod) ## extract the variance-covariance matrix head(vcov(dp))