Table 4 Rasch item and fit statistics for the 39 item Parkinson's disease questionnaire*.

	Item	Item statistics†		Fit statistics
		Location	SE	Residual‡	χ2§ ¶	F statistic¶ **
MOB	1	–0.51	0.10	2.02	4.17	1.67
	2	–0.26	0.10	–0.27	2.81	1.55
	3	–0.36	0.08	0.76	5.20	3.44
	4	–0.43	0.08	–0.08	1.36	1.05
	5	0.68	0.09	–0.55	7.45	4.77
	6	0.09	0.10	–0.17	1.58	1.00
	7	–0.24	0.10	–3.06	12.36	13.02
	8	0.15	0.08	–0.34	1.31	0.04
	9	0.53	0.09	2.26	3.50	1.64
	10	0.34	0.10	–0.30	1.30	0.74
ADL	11	0.79	0.09	–1.53	7.18	6.06
	12	0.22	0.09	–1.90	8.15	7.20
	13	–0.56	0.09	–0.66	4.16	2.98
	14	–0.89	0.09	1.59	6.82	3.54
	15	–0.07	0.09	–0.09	0.57	0.62
	16	0.51	0.09	2.86	12.41	4.87
EMO	17	–0.91	0.11	–1.73	3.99	3.30
	18	0.18	0.10	0.62	0.68	0.27
	19	1.22	0.11	1.98	1.97	0.88
	20	0.49	0.11	1.25	0.17	0.08
	21	–0.43	0.11	–0.57	2.83	1.81
	22	–0.55	0.11	0.68	0.44	0.25
STI	23	0.05	0.10	0.56	0.92	0.22
	24	–0.31	0.10	1.70	2.66	1.20
	25	–0.12	0.10	–1.10	7.77	6.90
	26	0.37	0.11	0.56	1.67	0.93
SOC	27	0.47	0.12	1.87	5.87	3.53
	28	–0.40	0.12	–0.87	7.06	7.13
	29	–0.07	0.11	–0.27	4.27	3.27
COG	30	0.59	0.08	1.65	0.75	0.27
	31	–0.59	0.09	–0.96	11.68	9.99
	32	–0.61	0.09	1.01	0.30	0.07
	33	0.60	0.09	1.11	1.32	0.64
COM	34	–1.03	0.12	–0.50	1.06	0.86
	35	–0.80	0.13	–2.25	8.17	10.78
	36	1.82	0.14	2.31	7.50	3.29
BOD	37	0.41	0.08	–0.19	7.15	5.59
	38	–0.42	0.08	–0.22	3.60	3.15
	39	0.00	0.08	1.34	0.04	0.02

ADL, activities of daily living; BOD, bodily discomfort; COG, cognitions; COM, communication; EMO, emotional well‐being; MOB, mobility; SE, standard error; SOC, social support; STI, stigma.

*Performed with the sample divided into three class intervals according to person locations on the measured variables. For details, see Tennant and colleagues,¹³ Hobart and colleagues¹⁴ and Andrich and colleagues.³⁰

†Expressed in linear log‐odds units (logits), with mean item location set at 0 for each scale.

‡Log residuals summarise the deviation of observed from expected responses. Deviation from the recommended range of −2.5 to +2.5,³⁰ indicating item misfit, are in bold typeface.

§χ² values summarise the deviation of observed from expected responses across the three class intervals of the sample. Higher absolute χ² values represent larger deviations.

¶Bonferroni corrected statistically significant deviations across class intervals, indicating item misfit, are in bold typeface.

**One way ANOVAs of deviations from model expectation across the three class intervals of people.