Validity and reliability of Work Productivity and Activity Impairment among patients with axial spondyloarthritis in Singapore.

OBJECTIVES

To assess the validity and reliability of the Work Productivity and Activity Impairment (WPAI) questionnaire in patients with axSpA.

METHODS

English-speaking patients seen at a dedicated axSpA clinic in a Singapore tertiary referral hospital were recruited from 2017 to 2019. Content validity of the WPAI was assessed through cognitive debriefing interviews (CDIs). Construct validity was assessed by a priori hypotheses regarding the correlations of the WPAI outcomes (absenteeism, presenteeism, overall work productivity loss, and activity impairment) with Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Patient Global Score (BAS-G), patient global assessment (PGA) and pain scores. Known group validity was assessed relative to disease activity. Test-retest reliability was assessed by intraclass correlation coefficients (ICC) in patients without treatment change 2 weeks apart.

RESULTS

Cognitive debriefing interviews conducted with 10 patients (22-46 years old, 50% male) supported the content validity of the WPAI. We analyzed cross-sectional data from 168 patients (mean [SD] age 41.0 [14.4], 79.8% male). Construct validity was established by meeting 100% of the hypotheses. Presenteeism, overall work productivity loss, and activity impairment demonstrated strong correlations with BASFI, BAS-G, PGA, and pain (rs  > .6). The WPAI was able to distinguish patients grouped by disease activity. Test-retest reliability conducted with 50 patients ranged from moderate to good for all the four outcomes (absenteeism: ICC = 0.54; presenteeism: ICC = 0.76; activity impairment: ICC = 0.79; overall work productivity loss: ICC = 0.83; all P < .01).

CONCLUSIONS

This study supports the content validity, construct validity, and test-retest reliability of the WPAI in patients with axSpA.