Discriminant validity, responsiveness and reliability of the arthritis-specific Work Productivity Survey assessing workplace and household productivity in patients with psoriatic arthritis

Table 6 WPS baseline scores assessed by defined known-groups: household productivity and daily activities (randomized set, observed cases)

Instrument^a	Number of days of household work missed over the previous month		Number of days with household productivity ≤50% at work over the previous month		Number of days of missed family, social or leisure activities over the previous month		Number of days with outside help over the previous month		Rate of arthritis interference with household work productivity over previous month^b
Instrument^a	Worse	Better	Worse	Better	Worse	Better	Worse	Better	Worse	Better
HAQ-DI	9.97**	1.60	11.97*	3.74	7.28**	1.43	4.82**	0.67	6.75**	3.22
(cutoff 0.88 and 1.75)	n = 116	n = 116	n = 116	n = 116	n = 116	n = 116	n = 116	n = 116	n = 116	n = 116
DAS28 (CRP)	8.44**	2.70	9.26**	5.60	6.00**	1.58	3.68*	1.07	6.11**	3.70
(cutoff 4.23 and 5.73)	n = 103	n = 101	n = 103	n = 101	n = 103	n = 101	n = 103	n = 101	n = 103	n = 101
SF-36 PCS	11.09**	1.37	10.81**	4.22	7.74**	1.37	4.65**	0.63	6.54**	3.30
(cutoff 27.99 and 38.28)	n = 101	n = 98	n = 101	n = 98	n = 101	n = 98	n = 101	n = 98	n = 101	n = 98
SF-36 MCS	10.10**	2.50	11.25**	5.19	7.91**	0.40	5.34**	0.18	6.65**	3.54
(cutoff 32.76 and 50.78)	n = 100	n = 101	n = 100	n = 101	n = 100	n = 101	n = 100	n = 101	n = 100	n = 101
PsAQoL	9.16**	1.70	11.44**	2.94	7.74**	0.35	4.97**	0.12	6.75**	3.04
(cutoff 6.00 and 16.00)	n = 104	n = 103	n = 104	n = 103	n = 104	n = 103	n = 104	n = 103	n = 104	n = 103
PASI	4.69	6.21	8.18	5.68	3.08	4.35	1.81	2.21	4.40	4.89
(cutoff 3.70 and 15.50)	n = 62	n = 66	n = 62	n = 66	n = 62	n = 66	n = 62	n = 66	n = 62	n = 66

Data presented as mean. DAS28(CRP), Disease Activity Score – 28-joint count based on C-reactive protein; HAQ-DI, Health Assessment Questionnaire – Disability Index; MCS, mental component summary; PASI, Psoriasis Area and Severity Index; PCS, physical component summary; PsAQoL, Psoriatic Arthritis Quality of Life; SF-36, Short Form-36 items; WPS, Work Productivity Survey. ^aCutoff points represent the first and third quartiles of baseline scores. Worse state defined for each individual measure as: DAS28(CRP) score ≥ third quartile, HAQ-DI ≥ third quartile, PsAQoL ≥ third quartile, SF-36 MCS ≤ first quartile, SF-36 PCS ≤ first quartile, PASI ≥ third quartile. Better state defined for each individual measure as: DAS28(CRP) score ≤ first quartile, HAQ-DI ≤ first quartile, PsAQoL ≤ first quartile, SF-36 MCS ≥ third quartile, SF-36 PCS ≥ third quartile, PASI ≤ first quartile. ^bWPS Question 4 is a 0 to 10 scale, where 0 = no interference and 10 = complete interference. **P ≤ 0.001. *P ≤ 0.01. ^#P ≤ 0.05. Nonparametric bootstrap t method with a variance stabilizing transformation, 10,000 replications.

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