An IERI – International Educational Research Institute Journal
Table 2 Bias and RMSE of Group Standard Deviation Estimates for DIF and nonDIF groups across the multigroup IRT models
| Â | Bias | Â | RMSE | Â | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Unadjusted | Adjusted | Unadjusted | Adjusted | ||||||||
Direction | Percent | Size | Type | NonDIF | DIF | NonDIF | DIF | NonDIF | DIF | NonDIF | DIF |
Positive | 10% | Small | Non | –0.91 | –0.67 | –1.48 | –1.03 | 5.04 | 4.97 | 5.06 | 4.73 |
|  |  |  | Uni | –1.22 | –1.53 | –0.60 | –1.16 | 4.97 | 5.42 | 4.95 | 5.29 |
|  |  | Large | Non | –0.79 | –0.03 | –1.11 | –0.47 | 5.38 | 5.13 | 4.92 | 4.99 |
|  |  |  | Uni | –0.47 | –2.17 | –0.36 | –0.84 | 5.16 | 6.95 | 4.75 | 5.28 |
|  | 20% | Small | Non | –1.04 | 0.32 | –0.78 | 0.84 | 5.08 | 4.68 | 5.35 | 5.60 |
|  |  |  | Uni | –1.38 | –2.76 | –0.09 | –1.38 | 4.85 | 6.48 | 4.95 | 6.38 |
|  |  | Large | Non | –1.12 | 0.62 | –0.76 | 1.47 | 5.12 | 5.11 | 4.99 | 5.35 |
|  |  |  | Uni | –0.98 | –4.65 | –0.60 | –1.81 | 4.91 | 7.91 | 5.13 | 5.82 |
|  | 40% | Small | Non | –1.48 | 1.13 | –0.79 | 1.30 | 5.07 | 5.11 | 4.82 | 5.35 |
|  |  |  | Uni | 0.20 | –1.73 | –1.04 | –2.81 | 4.73 | 6.40 | 5.06 | 7.44 |
|  |  | Large | Non | –1.22 | 2.20 | –0.74 | 2.80 | 5.36 | 6.25 | 5.40 | 5.74 |
|  |  |  | Uni | 0.17 | –5.83 | –0.79 | –8.19 | 5.31 | 10.16 | 5.28 | 13.95 |
Negative | 10% | Small | Non | –0.42 | –1.02 | –1.07 | –2.22 | 4.83 | 5.34 | 5.50 | 5.45 |
|  |  |  | Uni | –0.76 | –0.98 | 0.07 | –0.49 | 4.79 | 5.63 | 5.22 | 5.22 |
|  |  | Large | Non | –0.08 | –3.03 | –1.18 | –2.50 | 4.94 | 6.03 | 4.72 | 5.38 |
|  |  |  | Uni | –0.22 | –1.86 | –1.08 | –1.54 | 5.02 | 6.27 | 5.38 | 5.64 |
|  | 20% | Small | Non | –0.61 | –2.35 | –0.12 | –1.45 | 5.13 | 5.34 | 5.11 | 5.36 |
|  |  |  | Uni | –0.71 | –2.24 | –1.33 | –2.52 | 5.12 | 6.25 | 5.28 | 6.40 |
|  |  | Large | Non | –0.02 | –6.06 | –0.06 | –3.80 | 5.62 | 8.38 | 4.72 | 6.51 |
|  |  |  | Uni | –0.18 | –3.79 | –0.62 | –1.66 | 5.21 | 7.70 | 5.10 | 5.71 |
|  | 40% | Small | Non | –0.63 | –4.45 | –0.10 | –3.82 | 5.05 | 7.12 | 5.34 | 6.86 |
|  |  |  | Uni | –0.43 | –2.59 | –1.00 | –1.96 | 5.44 | 6.73 | 5.05 | 6.80 |
|  |  | Large | Non | –0.43 | –10.68 | 0.32 | –7.00 | 5.33 | 12.72 | 5.08 | 9.50 |
|  |  |  | Uni | –0.67 | –8.01 | –0.52 | –6.96 | 5.10 | 10.78 | 4.54 | 12.24 |