Table 2.

Average Bias, RMSE, and Standard Error of Focal Group Trait Estimates for 40-Item Tests.

		Deleting			Ignoring			Multiple-group			Modeling
No. of DIF items	Item discrimination for two dimensions	0	0.3	0.7	0	0.3	0.7	0	0.3	0.7	0	0.3	0.7
Bias
10%	Low α1 high α2	−0.031	−0.022	−0.009	−0.071	−0.092	−0.117	−0.030	−0.022	−0.010	−0.051	−0.060	−0.075
	Low α2 high α1	−0.031	−0.022	−0.010	−0.060	−0.052	−0.042	−0.033	0.022	−0.011	−0.057	−0.049	−0.039
	Moderate α1 and α2	−0.031	−0.023	−0.010	−0.076	−0.076	−0.074	−0.031	−0.024	−0.011	−0.064	−0.063	−0.061
30%	Low α1 high α2	−0.029	−0.020	−0.007	−0.226	−0.326	−0.007	−0.026	−0.022	−0.013	−0.063	−0.086	−0.130
	Low α2 high α1	−0.028	−0.020	−0.008	−0.147	−0.137	−0.008	−0.034	−0.025	−0.014	−0.118	−0.110	−0.106
	Moderate α1 and α2	−0.029	−0.021	−0.008	−0.238	−0.242	−0.008	−0.031	−0.025	−0.041	−0.107	−0.126	−0.132
	Average	−0.030	−0.022	−0.009	−0.136	−0.154	−0.042	−0.031	−0.016	−0.017	−0.077	−0.082	−0.090
RMSE
10%	Low α1 high α2	0.304	0.303	0.304	0.311	0.316	0.321	0.303	0.301	0.299	0.307	0.307	0.307
	Low α2 high α1	0.304	0.304	0.304	0.300	0.297	0.294	0.297	0.238	0.293	0.300	0.297	0.294
	Moderate α1 and α2	0.304	0.303	0.304	0.309	0.307	0.304	0.301	0.299	0.295	0.307	0.304	0.301
30%	Low α1 high α2	0.334	0.334	0.335	0.417	0.482	0.335	0.348	0.368	0.350	0.339	0.341	0.343
	Low α2 high α1	0.335	0.334	0.334	0.333	0.323	0.334	0.303	0.298	0.289	0.317	0.310	0.301
	Moderate α1 and α2	0.334	0.333	0.334	0.412	0.408	0.334	0.340	0.338	0.263	0.340	0.276	0.331
	Average	0.319	0.318	0.319	0.347	0.355	0.320	0.315	0.307	0.298	0.318	0.306	0.313
SE
10%	Low α1 high α2	0.314	0.315	0.317	0.315	0.314	0.306	0.311	0.310	0.308	0.318	0.318	0.313
	Low α2 high α1	0.315	0.316	0.318	0.303	0.302	0.302	0.307	0.304	0.308	0.304	0.303	0.302
	Moderate α1 and α2	0.315	0.316	0.317	0.310	0.307	0.303	0.310	0.310	0.308	0.314	0.311	0.306
30%	Low α1 high α2	0.347	0.348	0.349	0.347	0.327	0.349	0.338	0.338	0.321	0.351	0.350	0.339
	Low α2 high α1	0.347	0.348	0.350	0.301	0.296	0.350	0.305	0.302	0.299	0.312	0.306	0.295
	Moderate α1 and α2	0.348	0.348	0.350	0.328	0.313	0.350	0.326	0.321	0.330	0.345	0.350	0.323
	Average	0.331	0.332	0.334	0.317	0.310	0.327	0.316	0.314	0.312	0.324	0.323	0.313

Note. RMSE = root mean square error; DIF = differential item functioning.