itemfit.ppar {eRm} R Documentation

## Residuals, Personfit and Itemfit Statistics

### Description

pmat computes the theoretical person-item matrix with solving probabilities for each category (except 0th). 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. Corrected item-test correlations in itemfit are computed using the approach from Cureton (1966).

### Usage

## S3 method for class 'ppar'
pmat(object)
## S3 method for class 'ppar'
residuals(object,...)
## S3 method for class 'ppar'
itemfit(object)
## S3 method for class 'ppar'
personfit(object)
## S3 method for class 'ifit'
print(x, visible = TRUE,
sort_by = c("none", "p", "outfit_MSQ", "infit_MSQ", "outfit_t", "infit_t", "discrim"),
decreasing = FALSE, digits = 3,...)
## S3 method for class 'pfit'
print(x, visible = TRUE, ...)
## S3 method for class 'resid'
print(x, ...)


### Arguments

 object Object of class ppar, derived from person.parameter. x Object of class ifit, pfit, or resid. visible If FALSE, returns the matrix of fit statistics that otherwise would be printed. sort_by Optionally the itemfit output can be sorted by one of these criteria. decreasing If sort_by is set, whether the output should be sorted in increasing or decreasing order. digits How many digits should be printed. ... Further arguments passed to or from other methods. They are ignored in this function.

### Value

 pmat Matrix of theoretical probabilities for each category except 0th (from function pmat).
 i.fit Chi-squared itemfit statistics (from function itemfit). i.df Degrees of freedom for itemfit statistics (from function itemfit). st.res Standardized residuals (from function itemfit). i.outfitMSQ Outfit mean-square statistics (from function itemfit). i.infitMSQ Infit mean-square statistics (from function itemfit). i.disc Corrected item-test correlations (from function itemfit).
 p.fit Chi-squared personfit statistics (from function personfit). p.df Degrees of freedom for personfit statistics (from function personfit). st.res Standardized residuals (from function personfit). p.outfitMSQ Outfit mean-square statistics (from function personfit). p.infitMSQ Infit mean-square statistics (from function personfit).

### Author(s)

Patrick Mair, Reinhold Hatzinger, Moritz Heene

### References

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

Wright, B.D., and Masters, G.N. Computation of OUTFIT and INFIT Statistics. Rasch Measurement Transactions, 1990, 3:4 p.84-85

Cureton, E. E. (1966). Corrected item-test correlations. Psychometrika, 31, 93-96

person.parameter

### Examples


# Rasch model, estimation of item and person parameters
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)



[Package eRm version 1.0-2 Index]