Table 4.

Rasch item and fit statistics for the final ICF scales of the PDQ-39^a.

Component	Itemsb		Item statisticsc		Fit statisticsc			Total item-trait	PSIh
	No.	Content (abridged)	Locationd	SEd	Residuale	Chi squaref	F-statisticg	Chi-square (P-value)
BFa	17	Depressed	−0.65	0.11	−1.16	2.04	1.61	12.46  (0.41)	0.73
	22	Worried about the future	−0.31	0.11	0.53	0.77	0.39
	21	Anxious	−0.16	0.12	−0.74	1.88	1.44
	18	Isolated and lonely	0.42	0.10	0.52	0.51	0.18
	20	Angry or bitter	0.70	0.11	1.62	1.00	0.58
BFb	38	Pain in joints or body	−1.02	0.08	−0.21	0.29	0.18	6.15  (0.802)	0.88
	32	Poor memory	−0.46	0.09	0.94	1.04	0.62
	39	Unpleasantly hot or cold	−0.46	0.11	−0.15	2.21	1.31
	37	Painful cramps or spasms	−0.06	0.10	−0.63	5.28	3.72
	30	Unexpectedly fallen asleep	0.95	0.12	2.06	2.26	1.05
	33	Distressing dreams or hallucinations	1.05	0.12	0.13	1.38	0.82
APa	1	Leisure activities	−0.93	0.11	2.23	8.81	3.83	33.2  (0.007)i	0.96
	4	Walking half a mile	−0.79	0.09	0.59	2.16	1.34
	7	Getting around in public	−0.62	0.10	−2.36	3.43	3.51
	2	Looking after home	−0.60	0.10	0.92	2.47	0.93
	6	Getting around the house	−0.24	0.10	−0.57	2.22	1.44
	5	Walking 100 yards	0.45	0.10	−0.23	7.40	4.24
	12	Dressing	0.78	0.14	1.03	0.79	0.28
	11	Washing	1.95	0.14	−0.54	5.91	3.64
APb	14	Writing clearly	−0.77	0.09	−0.30	1.54	1.13	8.28  (0.60)	0.86
	13	Do buttons or shoe laces	−0.40	0.08	0.84	0.51	0.19
	15	Cutting food	0.01	0.09	−0.41	3.69	2.94
	16	Hold a drink without spilling	0.56	0.09	0.65	2.01	0.97
	24	Avoid eating/drinking in public	0.59	0.09	1.41	0.54	0.20
E	25	Embarrassed due to PD	−0.82	0.09	−1.27	1.86	1.27	13.42  (0.34)	0.82
	26	Worried about people's reactions	−0.41	0.10	−1.64	2.85	2.32
	23	Felt need to conceal PD	−0.20	0.16	−0.05	1.92	1.15
	36	Felt ignored	0.12	0.10	0.97	3.79	1.98
	28	Support from partner	0.38	0.18	1.25	2.73	1.28
	29	Support from family or friends	0.92	0.17	1.55	0.28	0.10

^aPerformed with the sample divided into three class intervals according to person locations on the measured construct.

^bListed in location order. Item numbers refer to the original PDQ-39 questionnaire. A total of nine original PDQ-39 items (numbers 3, 8, 9, 10, 19, 27, 31, 34, and 35) were excluded.

^cRounded to two decimals.

^dExpressed in linear log-odds units (logits). Mean item location is zero with positive values representing more health problems.

^eResiduals summarize the deviation of observed from expected responses.

^fChi-square values summarize the deviation of observed from expected responses across the three class intervals of people. Higher values represent larger deviations.

^gF-statistics from one-way ANOVAs of deviations from model expectation across the three class intervals of people.

^hReliability index analogous to Cronbach's alpha.

ⁱ P = .057 following Bonferroni correction.

ICF: International Classification of Functioning, Disability and Health; AP: Activity and Participation; BF: Body Functions and Structures; E: Environment; SE: standard error; PSI: person separation index.