personpar {psychotools} | R Documentation |
A class and generic function for representing and estimating the person parameters of a given item response model.
personpar(object, ...) ## S3 method for class 'raschmodel' personpar(object, ref = NULL, vcov = TRUE, interval = NULL, tol = 1e-8, ...) ## S3 method for class 'rsmodel' personpar(object, ref = NULL, vcov = TRUE, interval = NULL, tol = 1e-8, ...) ## S3 method for class 'pcmodel' personpar(object, ref = NULL, vcov = TRUE, interval = NULL, tol = 1e-8, ...)
object |
a fitted model object for which person parameters should be estimated. |
ref |
a vector of labels or position indices of item parameters
or a contrast matrix which should be used as restriction/for
normalization. If |
vcov |
logical. Should a covariance matrix be estimated (based on the joint log-likelihood) for the person parameter estimates? See also details below. |
interval |
numeric vector of length two, specifying an interval
for |
tol |
numeric tolerance passed to |
... |
further arguments which are passed to |
personpar
is both, a class to represent person parameters
of item response models as well as a generic function. The generic
function can be used to estimate the person parameters of a given item
response model.
Person parameters are estimated via uniroot()
with
the estimation equations given by Hoijtink & Boomsma (1995) as well
as Andersen (1995). This approach is fast and estimates for all
possible raw scores are available. If the covariance matrix of the
estimated person parameters is requested (vcov = TRUE
), an
additional call of optim
is necessary to obtain the Hessian.
With this approach, person parameters are available only for observed
raw scores.
For objects of class personpar
, several methods to standard
generic functions exist: print
, coef
, vcov
.
coef
and vcov
can be used to extract the
person parameters and covariance matrix without additional
attributes. Based on this Wald tests or confidence intervals can be
easily computed, e.g., via confint
.
A named vector with estimated person parmeters of class
personpar
and additional attributes "model"
(the model
name), and "vcov"
(the covariance matrix of the estimates if
vcov = TRUE
or an NA-matrix otherwise).
Andersen EB (1995). Polytomous Rasch Models and Their Estimation. In Fischer GH, Molenaar IW (eds.). Rasch Models: Foundations, Recent Developments, and Applications.
Hoijtink H, Boomsma A (1995). On Person Parameter Estimation in the Dichotomous Rasch Model. In Fischer GH, Molenaar IW (eds.). Rasch Models: Foundations, Recent Developments, and Applications.
o <- options(digits = 4) ## load verbal aggression data data("VerbalAggression", package = "psychotools") ## fit a Rasch model to dichotomized verbal aggression data and ram <- raschmodel(VerbalAggression$resp2) ## extract person parameters rap <- personpar(ram) rap ## extract variance-covariance matrix and standard errors vc <- vcov(rap) sqrt(diag(vc)) ## Wald confidence intervals confint(rap) ## person parameters for RSM/PCM fitted to original polytomous data rsm <- rsmodel(VerbalAggression$resp) pcm <- pcmodel(VerbalAggression$resp) cbind(personpar(rsm, vcov = FALSE), personpar(pcm, vcov = FALSE)) options(digits = o$digits)