data_sim_PCM {DIFtree} | R Documentation |

## Simulated Data Set with Polytomous Items

### Description

The data set is simulated from a Partial Credit Model
where some items exhibit differential item functioning.
Existing differences in item difficulties are simulated by step-functions.
The true, simulated DIF structure is described in Bollmann et al. (2017), Section 4.3.

### Usage

```
data(data_sim_PCM)
```

### Format

A data frame containing 500 observations on 4 variables:

**Y** matrix with categorical responses (3-point scale)

**x1** binary covariate

**x2** ordinal covariate

**x3** numeric covariate

### References

Bollmann, Stella, Berger, Moritz & Tutz, Gerhard (2018): Item-Focussed Trees for the Detection
of Differential Item Functioning in Partial Credit Models, Educational and Psychological Measurement 78(5), 781-804.

### Examples

```
data(data_sim_PCM)
Y <- data_sim_PCM[,1]
X <- data_sim_PCM[,-1]
apply(Y,2,table)
summary(X)
```

[Package

*DIFtree* version 3.1.6

Index]