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

Table 5 WPS baseline scores assessed by defined known-groups: patient workplace productivity (randomized set, observed cases)

Instrument^a	Number of days of work missed over the previous month		Number of days with productivity ≤50% at work over the previous month		Rate of arthritis interference with work productivity over previous month^b
Instrument^a	Worse	Better	Worse	Better	Worse	Better
HAQ-DI	3.51*	0.99	6.77*	3.17	5.71**	3.00
(cutoff 0.75 and 1.50)	n = 71	n = 78	n = 71	n = 78	n = 71	n = 78
DAS28(CRP)	3.54**	0.57	5.30	3.10	4.49^#	3.18
(cutoff 4.13 and 5.64)	n = 61	n = 61	n = 61	n = 61	n = 61	n = 61
SF-36 PCS	3.18*	0.87	6.85*	2.51	5.61**	2.69
(cutoff 29.56 and 40.43)	n = 61	n = 61	n = 61	n = 61	n = 61	n = 61
SF-36 MCS	2.89**	0.33	7.20**	3.03	5.32**	3.15
(cutoff 35.77 and 52.45)	n = 61	n = 61	n = 61	n = 61	n = 61	n = 61
PsAQoL	3.67**	0.47	8.11**	1.85	5.47**	2.71
(cutoff 6.00 and 15.00)	n = 61	n = 78	n = 61	n = 78	n = 61	n = 78
PASI	2.79	1.33	4.49	3.25	3.67	3.78
(cutoff 3.60 and 14.40)	n = 39	n = 40	n = 39	n = 40	n = 39	n = 40

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.

ISSN: 1478-6362