Table 7.
Fitting data generated from mixture IRT to unidimensional 2PL IRT model: Condition 2 (Increase in item discrimination for Group 1 at Time 2).
| Item | Time 1 | Time 2 | Change | |||
|---|---|---|---|---|---|---|
| a1 | b1 | a2 | b2 | a1 − a2 | b1 − b2 | |
| 1 | 0.94 (0.07) | −0.69 (0.06) | 1.48 (0.09) | −0.94 (0.07) | −0.55 | 0.25 |
| 2 | 1.65 (0.10) | −1.38 (0.08) | 2.20 (0.14) | −1.86 (0.11) | −0.55 | 0.48 |
| 3 | 1.09 (0.07) | −0.71 (0.06) | 1.65 (0.10) | −1.02 (0.07) | −0.57 | 0.32 |
| 4 | 1.38 (0.08) | 0.44 (0.06) | 2.02 (0.11) | 0.41 (0.07) | −0.63 | 0.03 |
| 5 | 1.71 (0.10) | 0.88 (0.07) | 2.47 (0.14) | 1.06 (0.09) | −0.75 | −0.18 |
| 6 | 0.85 (0.07) | −0.68 (0.05) | 1.40 (0.09) | −0.93 (0.07) | −0.55 | 0.25 |
| 7 | 1.76 (0.11) | 1.93 (0.10) | 2.27 (0.14) | 2.48 (0.13) | −0.52 | −0.55 |
| 8 | 1.79 (0.11) | −0.81 (0.08) | 2.21 (0.13) | −1.16 (0.09) | −0.42 | 0.35 |
| 9 | 1.83 (0.14) | −2.59 (0.13) | 1.76 (0.13) | −2.76 (0.13) | 0.07 | 0.17 |
| 10 | 0.99 (0.07) | −1.12 (0.06) | 1.59 (0.10) | −1.46 (0.08) | −0.61 | 0.34 |
| 11 | 1.03 (0.07) | −0.60 (0.06) | 1.52 (0.09) | −0.74 (0.07) | −0.49 | 0.14 |
| 12 | 1.09 (0.08) | 1.37 (0.07) | 1.26 (0.08) | 1.63 (0.08) | −0.17 | −0.26 |
| 13 | 1.48 (0.09) | 0.54 (0.06) | 2.13 (0.12) | 0.58 (0.08) | −0.65 | −0.03 |
| 14 | 1.50 (0.09) | 0.13 (0.06) | 2.06 (0.11) | 0.00 (0.07) | −0.57 | 0.14 |
| 15 | 1.19 (0.07) | 0.04 (0.06) | 1.77 (0.10) | −0.14 (0.07) | −0.58 | 0.17 |
| 16 | 1.47 (0.10) | −1.50 (0.08) | 2.28 (0.14) | −2.07 (0.12) | −0.81 | 0.57 |
| 17 | 1.40 (0.10) | 2.19 (0.10) | 1.52 (0.10) | 2.54 (0.11) | −0.12 | −0.35 |
| 18 | 1.72 (0.11) | 2.09 (0.10) | 2.03 (0.13) | 2.55 (0.13) | −0.31 | −0.46 |
| 19 | 1.86 (0.11) | 1.06 (0.08) | 2.64 (0.15) | 1.24 (0.10) | −0.79 | −0.18 |
| 20 | 1.50 (0.09) | 1.12 (0.07) | 2.06 (0.11) | 1.41 (0.09) | −0.56 | −0.29 |
Simulated with 100 replications using posterior mode estimation. Values in parenthesis represent standard errors.