Table 10.
Fitting data generated from mixture IRT to unidimensional 2PL IRT model: Condition 5 [increase in item discrimination and change in ability distribution for group 1 at Time 2 to θ~N(1,0.5)].
| Item | Time 1 | Time 2 | Change | |||
|---|---|---|---|---|---|---|
| a1 | b1 | a2 | b2 | a1 − a2 | b1 − b2 | |
| 1 | 0.94 (0.07) | −0.69 (0.06) | 1.42 (0.10) | −2.13 (0.10) | −0.48 | 1.44 |
| 2 | 1.65 (0.10) | −1.38 (0.08) | 2.75 (0.18) | −3.40 (0.19) | −1.10 | 2.01 |
| 3 | 1.09 (0.07) | −0.71 (0.06) | 1.89 (0.12) | −2.26 (0.11) | −0.80 | 1.56 |
| 4 | 1.38 (0.08) | 0.44 (0.06) | 2.79 (0.15) | −1.06 (0.10) | −1.41 | 1.49 |
| 5 | 1.71 (0.10) | 0.88 (0.07) | 3.10 (0.17) | −0.60 (0.10) | −1.39 | 1.49 |
| 6 | 0.85 (0.07) | −0.68 (0.05) | 1.31 (0.09) | −2.10 (0.09) | −0.46 | 1.42 |
| 7 | 1.76 (0.11) | 1.93 (0.10) | 2.54 (0.14) | 0.83 (0.09) | −0.79 | 1.10 |
| 8 | 1.79 (0.11) | −0.81 (0.08) | 3.66 (0.24) | −3.07 (0.20) | −1.87 | 2.26 |
| 9 | 1.83 (0.14) | −2.59 (0.13) | 3.14 (0.26) | −4.65 (0.32) | −1.31 | 2.07 |
| 10 | 0.99 (0.07) | −1.12 (0.06) | 1.38 (0.11) | −2.82 (0.13) | −0.39 | 1.70 |
| 11 | 1.03 (0.07) | −0.60 (0.06) | 1.39 (0.09) | −2.09 (0.10) | −0.36 | 1.50 |
| 12 | 1.09 (0.08) | 1.37 (0.07) | 1.29 (0.07) | 0.55 (0.06) | −0.21 | 0.82 |
| 13 | 1.48 (0.09) | 0.54 (0.06) | 2.69 (0.14) | −0.96 (0.10) | −1.21 | 1.50 |
| 14 | 1.50 (0.09) | 0.13 (0.06) | 2.85 (0.15) | −1.54 (0.11) | −1.35 | 1.67 |
| 15 | 1.19 (0.07) | 0.04 (0.06) | 2.38 (0.13) | −1.45 (0.10) | −1.19 | 1.49 |
| 16 | 1.47 (0.10) | −1.50 (0.08) | 2.30 (0.18) | −3.77 (0.21) | −0.84 | 2.27 |
| 17 | 1.40 (0.10) | 2.19 (0.10) | 1.57 (0.09) | 1.35 (0.08) | −0.17 | 0.84 |
| 18 | 1.72 (0.11) | 2.09 (0.10) | 2.13 (0.12) | 1.06 (0.09) | −0.41 | 1.02 |
| 19 | 1.86 (0.11) | 1.06 (0.08) | 4.18 (0.25) | −0.61 (0.13) | −2.32 | 1.67 |
| 20 | 1.50 (0.09) | 1.12 (0.07) | 2.41 (0.12) | −0.07 (0.08) | −0.91 | 1.19 |
Simulated with 100 replications using posterior mode estimation. Values in parenthesis represent standard errors.