data_sim_PCM {DIFtree}

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)