Table 3.

Item Parameters, Item Fit and Fixed Discrimination Results of MIRT Bi-factor Model

	General Factor	Sub-factor-Pain	Sub-factor - Fatigue	Step1	Step2	Step3	Step4	Item Fit*
neck stiff	1.615	0	0	−4.766	−4.078	−2.293	−0.225	1.98
body stiff	1.615	0	0	−2.85	−1.493	−0.189	1.517	3.91
arm stiff	1.615	0	0	−2.459	−1.518	−0.674	0.63	2.24
leg stiff	1.615	0	0	−1.343	−0.057	1.538	3.106	0.8
tired head up	1.615	0	1.117	−4.291	−2.795	−1.621	−0.245	2.2
tired sit	1.615	0	1.117	−5.264	−3.557	−1.404	0.343	−1.33
tired change position	1.615	0	1.117	−3.526	−2.868	−1.407	0.06	2.13
tired transfer	1.615	0	1.117	−3.32	−2.787	−1.092	0.584	3.67
tired stand	1.615	0	1.117	−3.496	−2.135	−0.28	1.441	2.05
tired walk	1.615	0	1.117	−3.766	−1.511	0.971	3.334	2.88
tired stairs	1.615	0	1.117	−3.476	−1.749	0.454	2.686	2.78
tired run	1.615	0	1.117	−3.328	−1.361	1.169	3.308	2.69
tired sports	1.615	0	1.117	−2.843	−1.733	0.508	2.292	1.5
tired fall	1.615	0	1.117	−4.28	−1.616	0.926	3.124	−1.31
tired get around	1.615	0	1.117	−5.98	−3.299	−0.399	2.002	3.54
tired at school	1.615	0	1.117	−5.68	−3.568	−0.694	1.729	3.16
tired homework	1.615	0	1.117	−4.804	−2.042	0.013	1.892	−2.56*
rest	1.615	0	0	−4.029	−2.916	−0.867	1.581	−0.9
tired after school	1.615	0	1.117	−5.477	−2.786	−0.157	2.118	1.24
tired missing school	1.615	0	1.117		−5.517	−3.694	−1.665	0.15
pain sleep	1.615	1.923	0	−7.776	−5.261	−2.925	−0.564	3.11
pain wake up	1.615	1.923	0		−5.927	−3.204	−0.726	2.32
pain sit	1.615	1.923	0	−7.055	−6.104	−3.63	−1.025	4.32
pain transfer	1.615	1.923	0	−6.947	−5.65	−3.716	−1.245	3.29
pain change position	1.615	1.923	0	−7.4	−6.247	−3.686	−1.212	3.79
pain stand	1.615	1.923	0	−6.226	−4.182	−1.72	1.04	4.28
pain move	1.615	1.923	0	−7.23	−5.209	−2.567	0.245	2.9
pain stairs	1.615	1.923	0	−6.108	−4.156	−2.071	0.28	4.97
pain running	1.615	1.923	0	−5.193	−3.741	−1.608	0.989	3.96
pain play	1.615	1.923	0	−6.278	−4.398	−2.002	0.772	2.19
pain riding	1.615	1.923	0	−7.815	−6.588	−4.188	−0.817	2.43
pain missing school	1.615	1.923	0		−7.201	−4.934	−1.967	0.47
tired indoor activity	1.615	0	1.117	−6.404	−4.856	−2.341	0.122	0.3
tired activity	1.615	0	1.117	−5.237	−3.256	−0.775	1.685	−0.28
pain wearing braces	1.615	1.923	0	−6.795	−4.447	−1.624	0.889	−1.85*
drool sit	1.615	0	0	−3.971	−2.881	−1.793	−0.862	2.35
drool activity	1.615	0	0	−4.251	−2.797	−1.839	−1	2.45

^*<−1.65 misfit