Table 2.
Correlation Between 1PL IRT and Parallel Fits, Data From 1PL IRT Model.
| Correlation in discrimination parameter |
Correlation in difficulty parameter |
Correlation in factor scores |
|||||||
|---|---|---|---|---|---|---|---|---|---|
| 1PL data vs. parallel fit | Minimum | Median | Maximum | Minimum | Median | Maximum | Minimum | Median | Maximum |
| Case 1 | • | • | • | 1.000 | 1.000 | 1.000 | 0.999 | 0.999 | 1.000 |
| Case 2 | • | • | • | 1.000 | 1.000 | 1.000 | 0.999 | 0.999 | 0.999 |
| Case 3 | • | • | • | 1.000 | 1.000 | 1.000 | 0.999 | 1.000 | 1.000 |
| Case 4 | • | • | • | 1.000 | 1.000 | 1.000 | 0.999 | 1.000 | 1.000 |
| Case 5 | • | • | • | 1.000 | 1.000 | 1.000 | 1.000 | 1.000 | 1.000 |
| Case 6 | • | • | • | 1.000 | 1.000 | 1.000 | 1.000 | 1.000 | 1.000 |
Note. 1PL IRT = one-parameter logistic item response theory. • = Discrimination parameter is not available in the 1PL IRT model, and loadings are not unique in the parallel model. With these models, the correlation is not calculated.