Table 8.
Fitting data generated from mixture IRT to unidimensional 2PL IRT model: Condition 3 (Increase in both item difficulty and 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) | 1.82 (0.10) | 0.23 (0.07) | −0.88 | −0.92 |
| 2 | 1.65 (0.10) | −1.38 (0.08) | 1.96 (0.11) | −0.42 (0.07) | −0.31 | −0.96 |
| 3 | 1.09 (0.07) | −0.71 (0.06) | 1.68 (0.09) | 0.16 (0.07) | −0.59 | −0.87 |
| 4 | 1.38 (0.08) | 0.44 (0.06) | 1.57 (0.10) | 1.59 (0.08) | −0.19 | −1.15 |
| 5 | 1.71 (0.10) | 0.88 (0.07) | 2.13 (0.14) | 2.48 (0.13) | −0.41 | −1.60 |
| 6 | 0.85 (0.07) | −0.68 (0.05) | 1.75 (0.10) | 0.20 (0.07) | −0.90 | −0.88 |
| 7 | 1.76 (0.11) | 1.93 (0.10) | 2.09 (0.17) | 3.88 (0.21) | −0.33 | −1.95 |
| 8 | 1.79 (0.11) | −0.81 (0.08) | 1.65 (0.09) | 0.15 (0.07) | 0.14 | −0.96 |
| 9 | 1.83 (0.14) | −2.59 (0.13) | 1.35 (0.09) | −1.62 (0.08) | 0.48 | −0.96 |
| 10 | 0.99 (0.07) | −1.12 (0.06) | 2.18 (0.12) | −0.19 (0.08) | −1.19 | −0.93 |
| 11 | 1.03 (0.07) | −0.60 (0.06) | 2.12 (0.12) | 0.48 (0.08) | −1.09 | −1.08 |
| 12 | 1.09 (0.08) | 1.37 (0.07) | 1.37 (0.11) | 2.56 (0.11) | −0.28 | −1.20 |
| 13 | 1.48 (0.09) | 0.54 (0.06) | 1.79 (0.11) | 1.84 (0.10) | −0.31 | −1.29 |
| 14 | 1.50 (0.09) | 0.13 (0.06) | 1.64 (0.10) | 1.24 (0.08) | −0.15 | −1.11 |
| 15 | 1.19 (0.07) | 0.04 (0.06) | 1.44 (0.09) | 0.98 (0.07) | −0.25 | −0.94 |
| 16 | 1.47 (0.10) | −1.50 (0.08) | 2.86 (0.17) | −0.48 (0.09) | −1.39 | −1.02 |
| 17 | 1.40 (0.10) | 2.19 (0.10) | 1.58 (0.14) | 3.53 (0.17) | −0.18 | −1.34 |
| 18 | 1.72 (0.11) | 2.09 (0.10) | 2.12 (0.18) | 3.97 (0.22) | −0.40 | −1.89 |
| 19 | 1.86 (0.11) | 1.06 (0.08) | 1.92 (0.13) | 2.58 (0.13) | −0.07 | −1.52 |
| 20 | 1.50 (0.09) | 1.12 (0.07) | 1.93 (0.13) | 2.74 (0.13) | −0.43 | −1.62 |
Simulated with 100 replications using posterior mode estimation. Values in parenthesis represent standard errors.