| MEASUREMENT PROPERTIES | |
| Limitations | <5 European languages (English) |
| Observations | |
| 1. RELIABILITY | |
| A. Internal Consistency | Not Tested |
| Cronbach's (Describe) | |
| B. Reliability intraobserver or test-retest | Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
A total of 50 patients with stable disease were assessed for test-retest reliability. Among the 50 patients, 32 (64.0%) were employed at baseline. Test-retest reliability conducted with 50 patients ranged from moderate to good for all the four outcomes with the following ICCs: absenteeism: 0.54 (95% CI: 0.24-0.78; P = .022), presenteeism: 0.76 (95% CI: 0.51-0.88; P = .001), activity impairment: 0.79 (95% CI: 0.63-0.88; P < .001) and work productivity loss: 0.83 (95% CI: 0.63-0.92; P < .001) when baseline data were compared with week 2 data. |
| C. Reliability interobserver or Measurement error | Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
After analyzing the baseline data with week 2 data, the SDC for absenteeism, presenteeism, work productivity loss and activity impairment were 6.6%, 24.9%, 19.3% and 24.3%. |
| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
The general WPAI was constructed such that it can be modified for any health problem by specifying the disease/condition of interest in the questions. Besides, cognitive debriefing interviews conducted with 10 patients (22-46 years old, 50% male) supported the content validity of the WPAI. |
| B. Construct Validity: Structural validity |
Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Tested |
| Brief Description |
Median scores for the ASQOL, BASDAI, SF-36 PCS and MCS, and HUI-3 were used to discriminate between patients with the worst health (worst AS disease severity) and those with the best health (least AS disease severity) at baseline. |
| C. Criterion validity | Not Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
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