itemfit.ppar {eRm} | R Documentation |

`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).

```
## 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, ...)
```

`object` |
Object of class |

`x` |
Object of class |

`visible` |
If |

`sort_by` |
Optionally the itemfit output can be sorted by one of these criteria. |

`decreasing` |
If |

`digits` |
How many digits should be printed. |

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

`pmat` |
Matrix of theoretical probabilities for each category except 0th (from function |

`i.fit` |
Chi-squared itemfit statistics (from function |

`i.df` |
Degrees of freedom for itemfit statistics (from function |

`st.res` |
Standardized residuals (from function |

`i.outfitMSQ` |
Outfit mean-square statistics (from function |

`i.infitMSQ` |
Infit mean-square statistics (from function |

`i.disc` |
Corrected item-test correlations (from function |

`p.fit` |
Chi-squared personfit statistics (from function |

`p.df` |
Degrees of freedom for personfit statistics (from function |

`st.res` |
Standardized residuals (from function |

`p.outfitMSQ` |
Outfit mean-square statistics (from function |

`p.infitMSQ` |
Infit mean-square statistics (from function |

Patrick Mair, Reinhold Hatzinger, Moritz Heene

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

```
# 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]