eRm (version 0.9-2)

itemfit.ppar: Residuals, Personfit and Itemfit Statistics

Description

pmat computes the expected person-item matrix with corresponding probabilities. residuals computes the squared and standardized residuals based on the observed and the expected person-item matrix. Chi-square based itemfit and personfit statistics can be obtained by using itemfit and personfit.

Usage

## S3 method for class 'ppar':
pmat(object)
## S3 method for class 'ppar':
itemfit(object)
## S3 method for class 'ppar':
personfit(object)
## S3 method for class 'ppar':
residuals(object,...)
## S3 method for class 'ifit':
print(x, ...)
## S3 method for class 'pfit':
print(x, ...)

Arguments

object

Object of class ppar, derived from person.parameter.

x

Object of class ifit, pfit, or resid.

...

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

Value

• Function pmat:
• pmat
  Matrix of theoretical probabilities.
• Function itemfit returns a list of class ifit with components:
• i.fit
  Itemfit statistics.
• i.df
  Degrees of freedom for itemfit statistics.
• st.res
  Standardized residuals.
• Function personfit returns a list of class pfit with components:
• p.fit
  Personfit.
• p.df
  Degrees of freedom for personfit statistics.
• st.res
  Standardized residuals.

References

Smith Jr., E. V., and Smith, R. M. (2004). Introduction to Rasch Measurement. JAM press.

See Also

person.parameter

Examples

# Rasch model, estimation of item and person parameters
data(raschdat2)
res <- RM(raschdat2)
p.res <- person.parameter(res)

# Matrix with expected probabilities and corresponding residuals
pmat(p.res)
residuals(p.res)

#Itemfit
itemfit(p.res)

#Personfit
personfit(p.res)