Table 4.

Mean bias and RMSE of the model parameter estimates for the mixture ERS-GPCM-CD on 6-point items.

Sample size	1000						2000
Response style	Normal		ERS		MRS		Normal		ERS		MRS
Criterion	Bias	RMSE	Bias	RMSE	Bias	RMSE	Bias	RMSE	Bias	RMSE	Bias	RMSE
PARAMETER
Test length = 20
Discrimination	0.019	0.079	—	—	—	—	0.004	0.051	—	—	—	—
Location	0.000	0.078	0.000	0.089	0.000	0.137	0.000	0.048	0.000	0.060	0.000	0.093
Threshold	0.000	0.126	—	—	—	—	0.000	0.079	—	—	—	—
$\overline{\theta }$	—	—	−0.002	0.079	0.027	0.088	—	—	−0.024	0.062	−0.014	0.075
Var(θ)	—	—	−0.054	0.200	−0.050	0.192	—	—	−0.016	0.140	−0.029	0.129
$\overline{\omega }$	—	—	−0.117	0.250	−0.104	0.137	—	—	−0.079	0.142	−0.038	0.076
Var(ω)	—	—	−0.012	0.095	−0.010	0.052	—	—	−0.031	0.083	−0.008	0.030
MDP	0.042	0.089	—	—	—	—	0.015	0.056	—	—	—	—
Test length = 40
Discrimination	0.028	0.072	—	—	—	—	0.008	0.046	—	—	—	—
Location	0.000	0.068	0.000	0.077	0.000	0.125	0.000	0.049	0.000	0.053	0.000	0.089
Threshold	0.000	0.111	—	—	—	—	0.000	0.076	—	—	—	—
$\overline{\theta }$	—	—	0.025	0.077	−0.006	0.067	—	—	−0.005	0.041	−0.007	0.058
Var(θ)	—	—	−0.035	0.147	−0.053	0.139	—	—	−0.005	0.094	−0.047	0.102
$\overline{\omega }$	—	—	−0.065	0.148	−0.085	0.113	—	—	−0.052	0.108	−0.050	0.074
Var(ω)	—	—	−0.003	0.066	−0.009	0.027	—	—	−0.021	0.063	−0.001	0.023
MDP	0.052	0.090	—	—	—	—	0.014	0.056	—	—	—	—

—, not applicable because of model constraints.