Table 3.

General Partial Credit Model (GPCM) parameters, and standardised loadings from confirmatory factor analysis for the 9-item Shared Decision-Making Questionnaire (SDM-Q-9)

Item no.	a	b1	b2	b3	b4	b5	Information	CFA loadings
1	0.22	4.50	0.42	−8.60	−4.83	−4.62	1.10	0.26
2	1.16	−1.73	−1.97	−2.59	−1.14	−0.93	5.80	0.72
3	1.34	−1.09	−2.40	−2.12	−2.14	−1.73	6.71	0.75
4	1.28	−1.51	−2.25	−2.72	−1.93	−1.73	6.40	0.67
5	1.15	−1.57	NA	−3.13	−2.36	−1.73	4.62	0.55
6	1.90	−1.83	−1.59	−1.61	−1.25	−0.74	9.48	0.87
7	3.41	−1.97	−1.53	−1.92	−1.18	−0.50	17.03	0.92
8	3.33	−1.83	−1.60	−1.79	−1.08	−0.39	16.66	0.92
9	1.52	−2.17	−1.48	−1.92	−2.11	−0.85	7.62	0.76

Goodness-of-fit indices for the CFA; CFI = 0.984, RMSEA = 0.069

Note a: discrimination parameter; b’s: threshold parameters; CFA: confirmatory factor analysis