Table 4.

Bias and RMSE of item parameter estimates under different combinations of knots and degree in bimodal case.

	a			b			c
	Bias	RMSE		Bias	RMSE		Bias	RMSE
2knots-degree3	0.078	0.304		−0.039	0.369		−0.011	0.080
2knots-degree4	0.084	0.311		−0.016	0.367		−0.015	0.081
3knots-degree3	0.095	0.324		0.048	0.363		−0.020	0.084
3knots-degree4	0.075	0.299		−0.016	0.374		−0.012	0.079
4knots-degree3	0.087	0.324		−0.039	0.429		−0.008	0.087
4knots-degree4	0.087	0.319		0.038	0.367		−0.017	0.084
5knots-degree3	0.071	0.303		−0.029	0.420		−0.011	0.087
5knots-degree4	0.076	0.304		−0.024	0.423		−0.008	0.086
6knots-degree3	0.073	0.310		−0.047	0.489		−0.010	0.087
6knots-degree4	0.082	0.310		−0.012	0.410		−0.013	0.084