eRm (version 0.9-2)

person.parameter: Estimation of Person Parameters

Description

Maximum likelihood estimation of the person parameters with spline interpolation for non-observed and 0/full responses. Extraction of information criteria such as AIC, BIC, and cAIC based on unconditional log-likelihood.

Usage

## S3 method for class 'eRm':
person.parameter(object)
## S3 method for class 'ppar':
summary(object, ...)
## S3 method for class 'ppar':
print(x, ...)
## S3 method for class 'ppar':
summary(object, ...)
## S3 method for class 'ppar':
plot(x, xlab = "Person Raw Scores", ylab = "Person Parameters (Theta)", main = NULL, ...)
## S3 method for class 'ppar':
logLik(object, ...)
## S3 method for class 'ppar':
IC(object)
## S3 method for class 'ppar':
confint(object, parm, level = 0.95, ...)

Arguments

object

Object of class eRm in person.parameter and object of class ppar in IC.

x

Object of class ppar.

xlab

Label of the x-axis.

ylab

Label of the y-axis.

main

Title of the plot.

...

Further arguments to be passed to or from other methods. They are ignored in this function.

parm

Parameter specification (ignored).

level

Alpha-level.

Value

• The function person.parameter returns an object of class ppar containing:
• loglik
  Conditional log-likelihood value.
• npar
  Number of parameters.
• niter
  Number of iterations.
• thetapar
  Person parameter estimates.
• se.theta
  Standard errors of the person parameters.
• hessian
  Hessian matrix.
• The function IC returns an object of class ICr containing:
• j.loglik
  Unconditional (joint) log-likelihood value.
• AIC
  AIC criterion.
• BIC
  BIC criterion.
• cAIC
  Consistent AIC criterion.

Details

If the data set contains missing values, person parameters are estimated for each missing value subgroup.

References

Fischer, G. H., and Molenaar, I. (1995). Rasch Models - Foundations, Recent Developements, and Applications. Springer. Mair, P., and Hatzinger, R. (2007). Extended Rasch modeling: The eRm package for the application of IRT models in R. Journal of Statistical Software, 20(9), 1-20. Mair, P., and Hatzinger, R. (2007). CML based estimation of extended Rasch models with the eRm package in R. Psychology Science, 49, 26-43.

See Also

itemfit.ppar,personfit.ppar

Examples

#Person parameter estimation of a rating scale model
data(rsmdat)
res <- RSM(rsmdat)
pres <- person.parameter(res)
print(pres)
summary(pres)
plot(pres)

#Person parameter estimation for a Rasch model with missing values
data(raschdat2)
res <- RM(raschdat2, se = FALSE)           #Rasch model without standard errors
pres <- person.parameter(res)
print(pres)                                #person parameters
summary(pres)
logLik(pres)                               #conditional log-lik value

#Extraction of IC's
IC(pres)