Table 4.

Power for Dichotomous Data.

	Iterative Wald approach								Wald-2 approach
Scale length	15 items				30 items				15 items				30 items
NR/NF	500/500	750/250	1,000/1,000	1,500/500	500/500	750/250	1,000/1,000	1,500/500	500/500	750/250	1,000/1,000	1,500/500	500/500	750/250	1,000/1,000	1,500/500
Compensatory DIF
% DIF = 0.2
DIF size = 0.3	.31	.25	.54	.45	.35	.29	.62	.52	.34	.27	.57	.47	.38	.30	.64	.54
DIF size = 0.5	.64	.54	.81	.78	.67	.58	.86	.80	.67	.57	.82	.80	.69	.60	.87	.82
DIF size = 0.7	.81	.74	.91	.88	.85	.78	.94	.91	.83	.76	.92	.89	.86	.79	.95	.91
% DIF = 0.4
DIF size = 0.3	.31	.24	.49	.46	.33	.27	.84	.78	.36	.28	.55	.49	.37	.29	.86	.80
DIF size = 0.5	.59	.51	.78	.73	.66	.57	.82	.77	.65	.55	.81	.76	.70	.60	.84	.78
DIF size = 0.7	.75	.68	.89	.85	.83	.57	.93	.90	.80	.73	.91	.88	.84	.60	.94	.91
Noncompensatory DIF
% DIF = 0.2
DIF size = 0.3	.37	.23	.68	.58	.32	.22	.57	.46	.40	.24	.71	.59	.34	.23	.59	.49
DIF size = 0.5	.72	.57	.90	.87	.68	.59	.87	.81	.76	.60	.93	.88	.70	.61	.88	.83
DIF size = 0.7	.86	.72	.96	.92	.84	.74	.95	.92	.89	.75	.98	.93	.86	.77	.96	.93
% DIF = 0.4
DIF size = 0.3	.22	.15	.49	.37	.22	.15	.41	.32	.24	.16	.53	.39	.23	.16	.43	.34
DIF size = 0.5	.49	.35	.73	.66	.49	.39	.70	.63	.53	.38	.81	.71	.52	.41	.72	.67
DIF size = 0.7	.64	.47	.80	.74	.64	.57	.82	.78	.72	.54	.90	.83	.68	.60	.87	.83

Note. DIF = differential item functioning; NR = number of respondents in reference group; NF = number of respondents in focal group; %DIF = percentage of DIF items.